These posts are all huge with images, wow.
Creature
Abyssal Persecutor
This card is the nuts. A 6/6 flying trample for 2CC.
Honourable Mentions:
Force of Savagery. This card has 8 power for only 2C.
Jace's Phantasm. A 5/5 flyer for C.
Ball Lightning. 6 power, trample, and haste for CCC.
Myr Superion. I can't believe I fogtot his guy until Leunam mentioned him. The Übermyr! a 5/6 for 2!
Artifact
Darksteel Relic.
The fact that cards like this can be printed, and actually be useful, shows how awesome of a game Magic is.
Honourable mentions:
Darksteel Citadel. The only artifact land that should have been printed.
Blacker Lotus. Might as well go all the way!
Equipment
Grafted Wargear.
Not much to say. Equip for 0, +3/+2, no real drawback.
Honourable mentions:
Basilisk Collar.
Deathrender. Even if you never use the ability, the fact that your opponent fears it enough to play around is great.
Enchantment
Grip of Chaos.
It mentions the stack in its actual text, what the hell.
Honourable mentions:
Food Chain.
Luminarch Ascension.
Manabond. Just because I like playing manlands.dec.
Aura
Angelic Destiny.
Flavourful, powerful. Should have been in AVR though.
Honourable mentions:
Ethereal Armor.
Animate Wall. For the art.
Instant
Dash Hopes
Almost everything that blue has, it has almost exclusively, counterspells included. Black and white should have more counterspells. Monoblack control should be a thing again.
Honourable mentions:
Fatal Frenzy. This is just 4 more copies of Ball Lightning.
Sorcery
Temporal Extortion.
Extra turns is another thing that blue has a stranglehold on. I don't know if they belong in black, but I'd like them in some non-blue colour. Also, I love CCCC costs.
Honourable mentions:
Heroes Remembered. "You gain 20 life", and it only costs C.
Reforge the Soul. I would like to put Wheel of Fortune, but I've never actually used one.
Land
Maze of Ith.
I strongly feel this card deserves a real reprint. Any environment with this card in constructed WILL have control decks, and they will be great. Maybe wait until some other great control cards (Sphinx's Revelation, Snappy) rotate, though.
Honourable mentions:
Creeping Tar Pit. My favourite manland.
Vesuva. Whatever you need it to be.
Planeswalker
Gideon, Champion of Justice.
It makes me sad that no one likes this guy. He has a +50 ability!
Honourable mentions:
Koth of the Hammer. The man likes him some mountains, and isn't afraid to admit it. I respect that.
Tezzeret, Agent of Bolas. I like cards that you have to build your deck around to use effectively.
Tezzeret, the Seeker. Same reason.
Whew. That took a while!