Oregon Trail (lol, I loved this game), the color one with "upgraded" graphics...
Glider (an easy, fun flying game with paper airplanes...)
Unreal Tournament - I still play facing worlds with buddies of mine, it's awesome...
Diablo I,II - I spent way too many hours on these games, II in particular...
Starcraft - I sucked at it, but it was fun.
Doom - this brings back fond memories... we went to the college in town and installed it on the lab computers, and we had to re-install every time since the IT department clean slated them every night... but oh so fun. We used to play Dead Simple for hours and hours...