Donkey Kong Country 2, possibly the greatest platformer ever as sub_tonic said, Final Fantasy 3 (6) is easily one of the best RPGs I've played, and Zombies Ate My Neighbors is classic co-op fun.
HA! Zombies ate my neighbors forgot about that, I loved that game also. I hated the damn level with the chainsaw guys...
Can someone help me remember a game? It was like a Pirates game either on the NES or Atari. It also might have been a black cartridge?
I'm also trying to remember a few games... anybody ever play that genesis game where your kind of like a mummy or something and after completing each level you a body part is added to create a monster or a Frankenstein type of thing I can't think of the name of this game... also kind of hard to describe...
Another one I'm trying to think of was some sort of game where your a robot with a sword and there was like a platform thingy that could be controlled by the 2nd player...