My Picks:

PC:
Action: Duke Nukem 3D
Strategy: Civilization
RPG: Fallout

Honorable Mention:
Quake, for being one of the first games that allowed for mods. Other than that I thought it was one of the worst games ever (Maybe it was because I was a Duke fan).
Half-Life, for being one of the best FPSers with a story and for having the Counter-Strike mod
Wolfensein 3D, For being the game that started FPSers in my mind, not DOOM.

Other
Commador 64: Predator & Blue Max

Whats yours?