Fallout 1, 2, 3 and new vegas.
Warcraft 3/TFT and any custom maps there within.
UFO afterlight.
Counter strike 1.6.
Battlefield 2.
Every single game of the total war series.
Colonization(ancient game but kickass).
Civilzation series.
Policequest all the way to swat.
Knights of the old republic.
Natural farm killers(haha such a hilarious game).
Deer hunter series.
Jagged alliance series.
The older Commandos games.
Corsairs(never found anywhere to buy or download this game fullversion
).
Hitman series.
Command and conquer series.
Delta force land warrior(mostly for lan awesomeness)
Grand theft auto 1 and 2.(newer versions dont feel right if not on console)
Some excellent free multiplayer games: Allegiance(space fighter/command/build simulator),
Call of combat(not for ragers, you will kill yourself, only reason I stopped playing was excessive raging..Awesome game and community)
Both games have rather small and devoted communities.
Ahh.. most of the games here have probly been mentioned, and there are so many more.. just cant think of them at the moment=/