Originally Posted by FngKestrel

A few have been already said,

Quake - Team Fortress, the original Canalzone 2 map was awesome.
Quake - Holy Wars. Great Deathmatch mode. Encourages team play and backstabbing in the same breath.
Half-life - TFC, pretty damn good remake IMO.
Half-life - Opera, love kung fu blood operas. Great take on the genre.
Half-life - Counter Strike naturally. But before bunny hoppers went insane.
Half-life - Yoda Deathmatch. Kind of odd, but for some reason, seeing Yoda's body sticking out of a wall is pretty damn funny.
BF1942 - Desert Combat, Stinger + Hind = Great fun.
Max Payne - Kung Fu. So good that the dev makers gave a shout out in the second one.