NES:
Bionic Commando
Ice Climber
Deja Vu, Uninvited, and Shadowgate (in that order) if you like Point and Click RPGs.
Adventures of Lolo
Mappy Land
Narc
Balloon Fight ftw!
River City Ransom
Snow Bros. kicks ass like Bubble Bobble, which you should also try
Adventure Island
Any of the Teenage Mutant Ninja Turtles games. :P
SNES:
Seiken Densetsu 3 if you're emulating. It's the best Mana game.
Indiana Jones Trilogy (and I'm not just saying that, I mean it)
Gundam Wing: Endless Duel if you wanna play a good Japanese fighter
Super Mario RPG
Street Fighter 2 whatever
Pocky and Rocky 1 and 2
Uhm... that's all I can think of (that isn't obvious) at the moment.
