Frogger is a classic, Galaga has already been mentioned as well as Dig Dug. No Pac-Man though? Come on people, I thought you people had more sense than that.

Jumping into the NES/Master System, you have to play Marble Madness, Ghosts'n Goblins, Disney's Adventures in the Magic Kingdom, Duck Tales, Darkwing Duck, Castlevania, Metroid, Contra, Mega Man 2, Altered Beast, Golden Axe, Battletoads, Nemo's Adventures in Dreamland, Master Blaster, Vectorman, Comix Zone, and of course, Legend of Zelda.