Neverwinter NIghts 2. Very well done, but I don't liek it's real time system nearly as much as I love turn based.
Temple of Elemental Evil, make SURE you get the Circle of 8 patch, to fix all the problems, and then it's the best D&D game, ever,
IMHO 
Pool of Radiance 2: Assault on Myth Drannot. this has got to be patched, or it cna wreck yer PC, lol, seriosuly.
Lot of folk don't like it, But I do.
Vampire the Masquerade: Bloodlines. 1st person RPG, very adult! again, get fan patch that fixes bugs, adds missing ocntent etc.
only "RPG" game i've ever seen in 1st person that really is a role playing game.
STALKER Shadow of Chernobyl. 1st person shooter, awesome, just awesome.
It also has the scariest,
wet pants making beasties, ever, oh and it's a D&D inspired beastie, too
If you've played it, youi know what I mean, hehe. That was really sick & evil to merge *beastie* with *effect*....
Oh and if you're British, get Judge Dredd versus Judge Death...just because hehe.