It's probably a shame that this thread isn't getting the attention it deserves, because I always made a point to visit the Card Ideas and Art section (one that I consider strictly inferior to the GS&F one) whenever I saw moomoose's name as the last poster.
I think Skinner's Pidgeon was what started it all - I love the blend of charm and randomness, while leaving it balanced and useable. And the 1% chances for either Adrenaline, Vampire, and one more that I've forgotten.
Mana worm also has to be one of my favourites up there, I like everything about it. Maybe not the artwork, but everything else.
Also very impressed with Pink Elephant.
And of course, the classics, Desync (extremely metaphoric really, especially considering the BL games I was playing) and Abomination, which sadly never made it into the game, or even the Armory, and like Van Goghs work wasn't appreciated where it was supposed to. Meaning, people seemed to like it more when they were in the humor section. Blah.