Coming late to this thread but I would say...
Pong
Space Invaders
Pac-Man (important nonviolent "cute" game)
Donkey Kong -- established platform genre & major franchise
Rogue -- template for all CRPG's to follow
Star Raiders -- first space sim
Flight Simulator
Ultima IV (most innovative CRPG IMHO)
M.U.L.E. or Archon -- taking multiplayer to the next level
Populous
SimCity
Civ
Dune 2
Doom
Quake
