Ultima IV: Quest Of The Avatar
The original Doom.
Anything with ZORK in the title, although Beyond Zork was probably the best of the lot. Actually, pretty much anything from Infocom.
KotOR 2. Probably the game I've replayed the most, overall,
<jmac7142> Most relationships exist despite being built on lies though. <El Sitherino>Yeah, and they usually involve freaky weird sex or money.