A fair number of the games mentioned here are available cheap on GOG.com so I thought I'd post links in case anyone wanted to pick one up. For anyone who doesn't know, GOG.com (Good Old Games) sells DRM-free games at a low price and has a lot of classic titles that have been tweaked to run on modern systems and they usually come with bonus stuff like sound track or concept art. Not to sound like a commercial, but in my opinion, GOG is one of the best things that has happened to computer gaming ever. They actually seem to care about giving customers an honest and good product for an unbeatable price. They're giving away Fallout 1,2 and Tactics for FREE right now.
Wizardry 6+7 8
Giants: Citizen Kabuto
Thief 1 2 3
Return to Krondor
Might and Magic 6 7 8 9
Arx Fatalis
The Longest Journey
Ultima Underworld
System Shock 2
Legend of Grimlock
Amnesia: The Dark Decent
Penumbra
Temple of Elemental Evil
Neverwinter Nights 1 2
Here's a few more that I think are all-time goodies
Beyond Good and Evil
Caesar 3
King's Bounty 1 2
Wizardry 6+7 8
Giants: Citizen Kabuto
Thief 1 2 3
Return to Krondor
Might and Magic 6 7 8 9
Arx Fatalis
The Longest Journey
Ultima Underworld
System Shock 2
Legend of Grimlock
Amnesia: The Dark Decent
Penumbra
Temple of Elemental Evil
Neverwinter Nights 1 2
Here's a few more that I think are all-time goodies
Beyond Good and Evil
Caesar 3
King's Bounty 1 2