In no particular order:
Asteroids (Atari 2600)
Space Invaders (Atari 2600)
Tetris (mainly NES, but I still play it on my cell phone daily)
Civilization (Amiga) (no, I didn't play it on the PC)
Castle Wolfenstein (C64)
Strategic Professional Football (C64) (It was a text based football game that my friends and I played religiously for years.)
Crimson Skies (Xbox)
Battlefield 2: Modern Combat (Xbox 360)