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I think that every color has a card that opitomizes it, that shows what it's about. Here's my list.

Blue-Force of Will : It shows blue's strongest suit, counterspells, and also shows the underhanded trickery inherent to blue. When needed, blue will sacrifice itself to bring the downfall of an opponent. Other possibles: Ancestral Recall

Red-Lightning Bolt: It's the most efficient creature kill spell in the game. Not even black has such a powerful spell in it's arsenal of creature kill. Lightning Bolt can kill 75% of the creatures in Magic, and that's saying a lot. Other Possible: Fireblast, Fireball, Pyroclasm

Black-Necropotence (and Yawgmoth's Bargain): This shows one of the staples of black's power, self sacrifice. Necro shows that black isn't afraid of loosing life, especially when it will help in it's struggle to defeat the opponent. Other Possible: Duress, Phyrexian Negator, Dark Ritual

White-Balance: Balance is the most powerful spell in the game, mostly because of it's supposed 'fairness'. Balance is a Wrath of God, Armegeddon, and Mind Twist all in one simple, 1W sorcery (plus, Stagg is in the picture, who could want more?). This shows how White isn't afraid of reseting the board, and making things fair. The lawful side of white allows for mass destruction, but only if it's both ways. Other Possibles:Serra Angel, Orim's Chant

Green-Ravenous Baloth: The Baloth displays one of greens greatest boons, efficiency. Green's creatures give the most bang for the buck, and are some of the best in the game. Baloth is one of the best creatures, pound for pound, in green. 4 for a 4/4 that allows you to sacrifice Beasts (one of greens major creature types) to gain 4 life. It's insane how good that is. Other Possibles: Bird of Paradise, Sakura-Tribe Elder

Gold-Pernicious Deed: More than likely one of the best mass-destruction spells, it shows how the two colors it uses (black and green) can coexist very nicely. The ability to destroy creatures (black), enchantments, and artifacts (green) in a tidy, 3 cost enchantment that can be controlled is unprecidented. Others: Vindicate, Terminate, Spiritmonger

Land-Cabal Coffers, Tolarian Academy, Gaia's Cradle, Serra's Sanctum, Balduvian Trading Post: Each of these lands, one for each color, all represent powerful aspects of their respective color. The only one I feel needs explaning is the Balduvian trading post. Red has a problem with protection creatures, and also has a problem with running out of damage. A land that can deal damage is the perfect solution to that problem, however, seems to warrant inclusion in any red deck that can run it.

Worst card ever! *drumroll*

Sorrow's Path
Land Rare The Dark
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Tap: Choose two target blocking creatures an opponent controls. If each of those creatures could block all creatures that the other is blocking, remove both of them from combat. Each one then blocks all creatures the other was blocking. Sorrow’s Path deals 2 damage to you and 2 damage to each creature you control.

First, to get the blocking to happen is nearly impossible to do. Unless you're opponent is chump blocking with something that's not important, but you don't care about killing it, and you want to kill the other thing your opponent is blocking with, and it's killable with the creature you want to block it with (assuming the opponent will block with a key creature, anyway).

Second, it turns into a Shock to you and a Pyroclasm to all your creatures, which is just bad bad bad. Most of the creatures played during that time were pretty small, and this card could kill all of them, especially after combat damage.

Exactly. Donate, whilst a very unique blue card, is not very representative of blue as a whole.

If you mean for the worst card ever? To be honest, even Donate has an application of some sort. Sorrow's Path just sucks.

no worst cards ever are the ones that had to have rules written just for them.
Choas orb.
Humility.
The "ante cards".
....... shall I go on?

lol

I think the dual lands are the best example for lands. They do what land are supposed to do. They give u mana and 2 kinds at that.
Blue: good ol' counterspell, not force of will. free spells dont really help describe a color.
Red: I agree bout lightning bolt.
Green: i think Kodama of the North tree is a prime spokesperson for G. Its big, its efficient, it has trample, and its ability says "cant touch this"
E. witness, Birds of paradise, and sakura tribe elder are good runner ups.
White: Auriok Champion. its cheap, its small, it has life gain, it has pro. black, and it has pro. red. that sums up what white is all about. Wrath of God, Final Judgement, Isamaru, Savanna Lions, and so on are good examples, but are lacking ever so slightly.
Black: animate dead, yawgmoths bargain, or phage. they are prime examples of what black is.
Artifact: The purpose of artifacts is to round out decks. One reason i hated affinity. so the best examples of artifacts i can think of would have to be Umezawa's Jitte or the Power Nine

thats why i chose what i did. even noob should know the cards i posted. by the way shock is the horribly watered down version of lightning bolt.

so for white you really mean storytelling (storyteller's?) circle

green-i would have to either go with kodaama of the north tree, or silvo's rogue elemental

red-kamahl pit fighter, or a fireball

blue-patron wizard, extract, or counterspell

white-humility, swords to plowshares, wrath of god, or pristine angel

black-dark ritual, vampiric tutor, or subversion

artifact-mycosnyth golem, myr incubator, or urza's incubator