Fallout 1&2 - just awesome, nothing else to say.
HOMM 3 - try a hotseat game with 4 friends... you'll need a lot of drugs against boredom.
Full Throttle - lol
Worms - everyone knows, everyone loves
Civ 2 - my favourite part of the whole series
Starcraft - you wanna count apm @ DotA? Haha...
Das Schwarze Auge 1,2,3 - from the german Pen&Paper RPG, very complex, takes a shitload of time to get through, but fun
Doom 1&2 - fuck Duke, fuck Quake, this is the real thing.
Torment - from the makers of Baldurs Gate, but A LOT better story and more interesting, the protagonist is a Zombie that wakes up in the mourge again every time you screw up (without your party ofc)
I'm sure I forgot things.