I'll recommend games to younger gamers but the graphics look like shit compared to today's games.
Unreal
Unreal Tournament (if you can find others to play with you)
Duke Nukem 3D
Sid Meyer's Civilization (the original one put out by Microprose. No addons. Just one complete game.)
Doom
Quake
Might & Magic (yes there is no "Heroes" in the title)
Baldur's Gate (The very first one)
King's Quest
Simon the Sorcerer
MDK (Murder Death Kill)
Orcs vs Humans (when Blizzard were not a corrupt asshole of a company)
No problem! You can purchase that hard to find cable at Radio Shack....Oh wait.