While I'm at it, I'll throw in some familiar faces and the trainers.
Ash is determined to win the Sinnoh League with just Pikachu and the Pokemon he catches in Sinnoh. He has gained a rival in the indifferent trainer Paul, a new friend in Dawn and reunited with Brock. Ash still tends not to think things through outside of battle that well and sometimes can seem more immature than Dawn, although by now he is considerably older. Ash's current Pokemon:
Pikachu is as determined as Ash to win the Sinnoh League and makes new friends among the Pokemon belonging to Ash, Brock, Dawn and other friendly trainers they meet. 
Starly was the first Pokemon in Sinnoh Ash captured. Sometime afterwards it evolved into a Staravia. Staravia is overly-dramatic and it's gender is undetermined. It can use Areal Ace and Wing Attack. Currently it wishes to learn Brave Bird. 
Ash's Turtwig has the same backstory as Bulbasaur in that it prevents Pokemon from fighting. It is a quite apologetic Pokemon yet also brave. When it wishes to show affection for Ash, it bites him on the head. It can use Razor Leaf, Bite, Tackle and Energy Ball. 
Chimchar was formerly Paul's Pokemon, and was often insulted and went through abusive training (though Paul said "Chimchar wants it this way", and Chimchar gave a confirming nod). Sick of how weak Chimchar seemed, Paul released it, despite Chimchar obviously pleading it would do better. Just as it was about to leave, Ash offered to be its trainer, and it accepted. Being with Ash has made Chimchar far happier than it was with Paul. It can use Dig, Flamethrower, Scratch, and Flamewheel. Team Rocket seem to be very fond of it. 
Buizel originally belonged to Dawn until she and Ash traded. Buizel is very proud of his power and skill, and took his first loss hard. He can use Aqua Jet, Silver Wind and Water Gun. 
Out of all the Gligar that followed the Gliscor Paul hunted, one that had a habit of winking, licking its lips, and always oblivious to when its fellows took off became Ash's six Pokemon. So far it hasn't been seen battling, so it's attacks are unknown.
James still seems to be Jessie's easily intimidated partner, but during his time in Sinnoh gives Cacnea to Gardenia for training, showing emotional growth on his part. 
James' Pokemon:
Mime Jr. continues to be Jame's favorite Pokemon after Chimecho.
James had Carnivine since he was little when his family traveled to their summer "cottage" in Sinnoh and reclaimed it when TR arrived in the region. Like Victreebel, Carnivine bites James before obeying orders, though more out of being reunited with James than a lack of training. It can use Wrap, Bite and Bullet Seed, it's most used attack. 
Jessie is still determined to become a world famous Coordinator and has entered local contests under the guise "Jessilina". She deeply resents Zoey for beating her in her first Sinnoh contest and has a one-sided rivalry with Pokemon Hunter J. Jessie's Pokemon:
Like Meowth, Wobbuffet seems to gain more human traits than a regular Pokemon, such as helping Team Rocket "drive" one of their vehicles. He is still called on for his Counter and Mirror Coat attacks, however. 
After Ash gained Chimchar, Seviper sensed the precense of three Zangoose and repeatedly attacked and was attacked, despite Jessie calling it back to its Pokeball. While it had stagefright the first time she tried to use it in a contest, it did much better in an appeal round of Jessie's second Sinnoh contest. 
Dustox continues to be Jessie's primary contest Pokemon. It proved to withstand Piplup's Bide in her second contest. 
Brock showed up with a trucker girl (and was horrified that she already had a boyfriend after buying her dinner) in Sinnoh. After being "dumped", he decided to join up with Ash after finding him on the side of the road with Aipom. His goal is still to be a master breeder. Funnily enough, the only two girls in Sinnoh who've fallen in love with him were girls he didn't flirt with (although the first said she wasn't "interested in younger men" wink . Brock's Pokemon:
Bonsly was the only Pokemon Brock brought to Sinnoh, much like how Foretress was the only one he brought to Hoenn. Bonsly evolved into Sudowoodo when it and Brock tried to help save a Nuzleaf from Team Rocket. As a Sudowoodo, it proves to be very strong with its Mimic attack. It tends to salute when called out and has a bounce-back personality. 
Croagunk was previously used by Jessie, but chose to become Brock's Pokemon when she abandoned it. It knows many Fighting-type attacks such as Brick Break and its signature attack is Poison Jab. When Brock starts to flirt, Croagunk tends to jab him in the back or the stomach. Some suggest Croagunk is female and may have a crush on Brock, explaining why it jabs him. 
Brock's Happiny is the Sinnoh Togepi. She is very fond of Brock. Although she is tiny, Happiny can pick up and hurl a person, or carry a stack of bricks in one little hand. 
Dawn is a new pokemon trainer and daughter of a pokemon cordinator Johanna. Dawn hopes to follow in her mother's footsteps and always enjoys entering any kind of contest. Dawn is big on fashion and looks, and loves to wear elaborate costumes whenever she can, mostly during pokemon contests. She could be referred to as a Sinnoh version of Ash, but rarely looks back at her past mistakes. Like Ash, Dawn has a rival of sorts in her old preschool friend Kenny who calls her Dee When Ash has a gym battle, Dawn will sometimes wear a cheerleader outfit and cheer Ash on with Piplup and Buneary.
Her current Pokemon:
Piplup was her first Pokemon, though did not want to obey her until she saved it from an Ariados' web. It's a very proud little Pokemon and can be headstrong and arrogant, but also easily makes friends when it can. Piplup can use Bubble Beam, Bide and Whirlpool.
Much like how Misty wanted a Corsola, Dawn wanted a Buneary after seeing one, but failed various times. A female Buneary developed a crush on Ash's Pikachu before Dawn captured her. At times Buneary will blush if Pikachu talks to her. Buneary can use Bounce, Ice Beam, and Dizzy Punch (with one of her ears).
Dawn became smitten with the cuteness of Pachirisu, but felt it was too much for her to handle as it would run about randomly and use Spark without warning. She temporarily released it, then after some soulsearching took it back. Pachirisu is one of the younger main Pokemon. 
Ash's Aipom came with him from Kanto. Because of Aipom's apparent love of Pokemon Contests, Ash and Dawn traded Pokemon; Ash got her Buizel, Dawn got his Aipom. Soon after becoming Dawn's Pokemon, Aipom evolved into Ambipom after learning Double Hit.Dawn has a rival in a childhood friend named Kenny, primarily due to his semi-constant teasing, reflecting on when they were in preschool together which leads to embarrassing stories for Dawn, and calling her "Dee-Dee"; yet some fans speculate Kenny has a slight crush on Dawn because of this. Perhaps to go with how Dawn looks in her contest dress, Kenny has an outfit that makes him resemble a young prince. Whereas Ambipom is the only evolved pokemon Dawn has at the moment, all of Kenny's pokemon are evolved.
Kenny's Pokemon:
Kenny's signature Pokemon. Can use Metal Claw. Is the evolved form of Piplup. 
Although intimidating in battle, Kenny's Alakazam has only been seen in an appeal round of a Pokemon Contest using Kenisis, Protect and Shadow Ball.
Kenny's Breloom is capable of using Energy Ball and Stun Spore. 
Paul has a very cold attitude when it comes to pokemon; he is uninterested in "weakling" pokemon and promptly releases those he dubs as such. Ash and Brock encountered Paul after he had used his Elekid to capture three Starly, released two, used the remaining Starly to battle the one Ash had captured, and released it on the grounds it wasn't worth his time training. He presumably acquired the Chimchar that stole food from Piplup, and is very hard on it, viewing it as weak. Paul's training methods and views on pokemon greatly antagonize Ash, whom he views as weak. He sought out Cynthia of the Sinnoh Elite Four and challenged her to a battle, probably seeing her as a likely equal due to his arrogance, and lost to her. Most of Paul's Pokemon don't seem to care about his harsh personality (his Elekid/Electabuzz mirrored him somewhat) and probably only view him as a human who can make him stronger just as he views them in his goal to become a stronger trainer. Chimchar is as of yet the only Pokemon who couldn't withstand the training, being more gentle than Elekid, Ursaring and Torterra, though Chimchar confirmed it wanted harsh treatment to increase its strength when Paul said so.
His current Pokemon:
Paul captured an Ursaring in Bewildered Forest and decided to keep it. His Ursaring can use powerful Fighting-type moves like Focus Blast and Hammer Arm. Whether or not it knows the moves naturally or from training isn't revealed. 
Paul used a Weavile against Cynthia's Garchomp using Blizzard and Ice Beam and was also used in capturing Gliscor. Exactly where, when and if it was a Sneasel when Paul captured it is unknown. 
Paul used a Murkrow against Cynthia's Garchomp using Haze and Sky Attack. It was later seen using Shadow Ball on Chimchar and flying among a group of Gligar. Paul may have used a Dusk Stone to evolve it into a Honchkrow offscreen. After evolving, it beat Maylene's Meditite and drew with her Machoke. 
Paul's starting Pokemon was a Turtwig that evolved into a Grotle then Torterra offscreen. Torterra seems to mirror Paul's desire for perfect victory and strong opponents. It can use Frenzy Plant, Giga Drain, Hyper Beam and Leaf Storm. 
Gliscor became Paul's target for unknown reasons, being hunted by him with Weavile. While Paul captured Ursaring without trouble, Gliscor proved to be the sort of Pokemon that grabs his attention in terms of power and intelligence. It can use X-Scissor. 
Paul traded in his Electabuzz for his Magmar when reaching his hometown Vielstone City. It was able to beat Maylene's Lucario with Firespin and Fire Punch. 
Elekid was very much like an arrogant counterpart to Pikachu and seemed to share Paul's view that Ash and Pikachu were pathetic. It seemed to be favored over Chimchar. Elekid evolved into Electabuzz and afterwards used to help capture Gliscor. It was then left with Reiji to train.Paul abandoned his Chimchar after concluding that he needed "a stronger Fire-type and it's implied he has more than just six Pokemon. It's more or less confirmed when he visits his brother Reji in Veilstone and exchanges his Electabuzz for his Magmar. After defeating the gym leader Malyene with his newly-evolved Honchkrow and Magmar, he insulted her and further shattered her confidence. Paul has a Pokemon Breeder for a brother named Reji. Reji has participated in all the Pokemon Leagues and gained all Frontier Symbols. Perhaps this sheds some light on Paul's attitude; having to live in his brother's shadow.
Nando is a recurring character in the stereotypical fashion of a wise wanderer. He chooses to be both a battling trainer and a contest trainer. Nando had a Budew before it evolved into a Roselia. Nando's Pokemon:
Budew evolved during a battle with Pikachu, and for the most part goes around outside of it's Pokeball. It can use Sunny Day, Solarbeam and Bullet Seed. 
Nando's Sunflora can use Grass Whistle. It was used alongside his Krickitune in Hearthome City. 
Nando used his Krickitune in the Hearthome City Pokemon Contest with his Sunflora. It used Sing to compliment Sunflora's Grass Whistle.
Zoey is a pokemon cordinator who admires Dawn's mother Johanna and perhaps chooses a Glameow as her primary contest pokemon. Like Dawn, Zoey dons an elaborate costume that some fans say gives her a masculine appearance. In their first meeting, Zoey behaved very openly and in a friendly manner towards Dawn upon learning it was her first contest, but was critical of Ash on the grounds that he was treating the upcoming contest battle like a gym battle. She battled Ash and his Aipom with her Glameow, both trainers being startled by their unconventional moves and battle style, admitting afterwards that if time hadn't run out earning Zoey the win, Aipom might have beaten Glameow, then made the strange suggestion that Dawn raise Aipom instead. She next appeared after hearing rumors of an aggressive Buizel and remarked "Gee, Dawn, you sure have some interesting friends" after seeing Ash, Pikachu and Piplup trying to train with Buizel. Jessie greatly resents Zoey for beating her in her first Sinnoh contest battle. Although they are technically rivals, Zoey and Dawn treat each other as best friends. Zoey's Pokemon:
Zoey's signature Pokemon, and possibly her strongest, as it rarely loses a battle. It is capable of using Shadow Claw, Iron Tail, and Shock Wave.
Zoey's Misdreavus is a mystery as it's only been seen in her debut using Double Team and Thunder as an appeal for a contest. 
Shellos is Zoey's third Pokemon, and apparently somewhat babied by Zoey. It can stretch it's neck, use Mud Shot, Blizzard and Hidden Power. 
J is an infamous and frighteningly successful pokemon hunter/poacher to rival any before her. Like previous antagonists, J thinks nothing short of stealing the pokemon of other people or any other pokemon unfortunate enough to cross her path she believes may make her a lot of money--such as Pikachu for his high power and Meowth for his ability to talk--and is seemingly impossible to catch by some mysterious technology that allows her airship to camoflauge itself against the sky. J also seems to view her henchmen as expendable, as she abandoned a minority of them when Ash and Team Rocket laid siege to her airship to rescue Pikachu and Meowth and allowed them to be captured by the resident Officer Jenny for their crimes. J's Pokemon:
Her Drapion is her main battler and seems almost invincible. It can use Poison Sting and Cross Poison.Sinnoh Now is a popular TV show in Sinnoh, hosted by Rhonda. Her attire, hair/hair color, and sometimes temper make her resemble Naru Narusegawa from Love Hina. Wherever there is a story, it's a safe bet that Rhonda and her crew will be on the scene. Rhonda seems to have an intimidating relationship with her boom operator Jack due to a running gag of Jack of being unable to hold the boom microphone and hitting her in the head while she's talking, leading her to state "Do that again and it's back to the mail room!"
Gardenia is a recurring gym leader specializing in Grass-types. Perhaps to parody Misty's love for Water-types, Gardenia is obsessed with grass-types; in fact, when she first set eyes on James's Carnivine she went gaga over it and had a strange almost orgamisc reaction to Cacnea's Pin Missile in her back, driving James nuts. She came out of her crush long enough to beat Team Rocket with her own Turtwig when they tried kidnapping Cheryl's Mothim. Her first battle against Ash was short, beating Turtwig and Staravia despite the type advantage for the starling pokemon. 
Cacnea is with Gardenia in training to use Drain Punch. This may be the writer's answer to avoid Cacnea evolving. 
Team Galactic could be considered to be like Team Rocket, Team Aqua and Team Magma before them, led by their leader who seeks to make himself a god via use of Palika and Dialka, pokemon that can allegedly alter time and space. The main agents are named after planets; Mars, Saturn, and Jupiter. They are led by Cyrus.In the games Team Galactic operate openly, as their leader makes no attempt to hide his identity, as though they are unopposed by the law, even having a building and warehouse in Veilstone City. To further their daring, they will openly request pokemon in TV prodcasts. Both the commanders and grunts have faintly any understanding of their boss, most of all Saturn, who follows Cyrus merely for the idea of a new world. The grunts believe their goal is to collect and horde rare pokemon. Most grunts will have Beautifly or Clefairy, though this hasn't occurred in the anime, and most agents have Bronzor.
In the Anime, they are more secretive, the first time Saturn and two grunts commissioned Team Rocket to steal the Adamant Orb from the Eterna City Museum, no doubt to control and amplify the power of Dialga, but the trio were unsuccessful.
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