I missed many great games, but from those I didn't ;-)
1. Starcraft - half a year taken from my life (mostly nights), plus some eyes problems
added ;-) ..Once 3rd on the worldwide ladder... but in beta and without crazy koreans ;-)
2. Baldur's Gate - somehow first RPG I finished, lots of emotions and memories (especially when I decided to complete most of the game as one character for
faster exp gathering;-)
3. Call of Duty 2 - small revange for WW2;-)

UFO: Enemy Unknown
Fallout
Blade Runner (I JUST LOVE THIS GAME!)
Btw - just 3? It should be top 5 or top 10! :(
Acctually I have like top 20 :D

Quake II (CTF MOD) - got me into online FPS gaming, now I'm addicted. :)
PlanetSide - the only game of its kind, the best gameplay design , the only FPS with a real goal (ending the map/being the first on the list is no goal), severe lag issues (which never got fixed while I was playing) and inadequate marketing. PlanetSide deserved so much more... :/
Team Fortress (Quake 1 MOD) - I was only a 36k HPB when I first tried this game and it was awesome. Later TFC came out and I had a lot of fun with clan wars. Then Team Fortress 2 came out, open servers were fun, but clan wars were boring... And it all started with a little mod for a big game :)

Wow... all time, all systems... that would take me way too long to figure out -- it'd be some sort of 128-game March Madness-style battle royal to the death... soo... off-the-cuff:
1. Super Mario 3 (NES)
2. Tie Fighter (PC)
3. Diablo (PC)