The thing that first introduced me to the Red Panda and other modern radio shows was a directory when I was looking for things to listen to when I drove down from college. The directory is not complete, but it does give you an idea of what is out there.

The Red Panda
The Red Panda takes place in 1933. The Red Panda is a combination of Bruce Wayne, the Green Hornet, and the Shadow. The Flying Squirrel is a wonderful addition. Decoder Ring Theatre does a wonderful job of creating strong women in eras that women didn't have much power in society. The Flying Squirrel is more like the Red Panda's partner than his sidekick by the second season, and is truly his partner by the third season. They only keep up the pretense of 'sidekick'. The Flying Squirrel is more terrifying to the average criminal than the Red Panda. She's awesome!
There are 12 episodes to a year, and the timeline is consistent. The release date is also consistent.

Black Jack Justice
Trixie is another perfect example of Decoder Ring Theatre's knack for strong female characters. She and Jack are the perfect examples of siblings. I think that the phrase "My least favorite brother" is the perfect way to describe their relationship. Trixie is also way more hard boiled than Jack, who is more like a jaded hopeless romantic. His feelings for Trixie are slightly more obvious, while Trixie's actions speak louder than her words. She never comes out and says how much she cares about Jack, but her actions in "Journey's End" (episode 36) and "the Score" (episode 45).
Black Jack Justice, the first season was 12 episodes, and the ones after are 5 episodes.

Star Trek: Excelsior
I am... not much one for fan fiction. However, I have found that audio show fan fiction is closer to the medium of television and is superior. Star Trek: Excelsior, also known as Starship Excelsior (which is what the podcast is called), is a complex and excellent show. The first season is fast, the second season is strong and the third season is intense. In fact, I recommend an entire day be set aside for the second half of the third season. Unfortunately, I cannot go into to much detail about the show because of it's immense complexity. One of the crew has a saying "Wheels within wheels", and perfectly applies to the show. My favorite character is Rol, followed closely by Lorhrok.
The pilot must be downloaded, or found at the site because the producer is quite simply embarrassed by their venture in audio shows. He thinks that you don't have to listen to it to understand what's going on. I think that the introduction of characters in the pilot makes everything much clearer. I had Ccarlet listen to the pilot first, and she agreed with me. It does get better as it goes.

Star Trek: Outpost
Welcome to DS3, one of the most raggedy outposts of StarFleet, and newly promoted Lt. Commander Greg Torkelson's new posting as second in command. The final stationing of misfits, almost slackers, and eccentrics, Deep Space 3 is on the boarder of Ferengi space, an area of Bermuda Triangle like space known as the Pinch, and any manner of rogues and pirates who make this frontier their home. Is it possible to bring the station back together? Or will its own captain be its undoing through a drive for efficiency?
Not as good as Excelsior, but it is released once a month. Which is most impressive for a fan production. There are some actors from Excelsior on this show. Good character arc for a few characters. It is a bit slower than I like. The characters alternate between very interesting and compelling, and vaguely dull.

BrokenSea Audio Productions
I'm just clumping these shows into one section. They've done quite a few. I prefer Jake Sampson: Monster Hunter and Maudelayne.
Jake Sampson: Monster Hunter is a bit more serious. It is more than a little campy, takes place in 1936 or so. I rather like the relationship between Jake and his friends. Which develops slowly, but is what ultimately gained my attention.
Maudelayne is about three college boys in the year 1933, and is fairly light hearted. Joking really. The relationship between the boys is adorable. My favorite is John Westbrook, the only American.
These productions are of varying quality. To be quite frank, I'm not entirely sure whether the distortion of certain actor's voices is intentional or a side effect of recording in different conditions. Sometimes the distortions are quite bad. I am not in love with any of the stories. They are merely a diversion to me. But the character chemistry is subtle and I appreciate it. The other reason to acknowledge BrokenSea is their wide range of genres, and accessibility to different tastes. They have shows that range from family friendly such as Maudelayne, to explicit such as Voyage to Gaia.
I am not invested in their shows, and would not actively recommend them to my friends, given how many dramas I already want them to listen to.