There is a lot of great games.
To be honest, i don't even play on my pc games newer than 2005/6 (with some exceptions). I don't know what type of games do you like, so here's my list (not alphabetical or something, i'll just write while thinking).
- Carmageddon 1 and 2, great combat racing games,
- Rally Trophy, fantastic old racing game,
- Soldier of Fortune 1 (and maybe 2), solid, but a little bit brutal fps,
- Arcanum, amazing rpg,
- Jagged Alliance 2, tactical strategy mixed with rpg, one of my favourite games of all time,
- Commandos 1/2, mission-based rts
- Desperados - Wanted Dead or Alive, just like Commandos on Wild West. Absolutely amazing game,
- Capitalism 2, economic strategy,
-Tropico 1, as above,
- Giants - Citizen Kabuto, action game with great humour,
- Max Payne 1 - legendary action game,
- Serious Sam First Encounter - freaky but great fps,
- Tomb Raider 2-4, everyone knows it but hey, they are great games!
- Need for Speed Porsche Unleashed, one of the best NFS games,
- Gorky 17, polish post-apo rpg, fantastic game,
- Gangsters: Organized Crime, old but good strategy game with "Godfather" sense,
- Hexen 2 - really oldschool, but great fps,
- Shogun Total War - stunning rts,
- Homeworld - as above, but in space,
- Fallout 1/2/Tactics, post-apo rpg (Tactics is more like mission-based tactical strategy),
- Anno 1602/1503 - economic/rts/creating a new world,
- Puzzle Quest - mix of rpg and puzzle game,
- Warcraft 3, Metal Fatigue, Total Annihilation - all of them are absolutely fantastic rts games,
- Space Rangers 1/2, maybe they will work, because i played them on my low-specs laptop some time ago,
- Port Royale, something like Anno mixed with Pirates,
- Star Wars Jedi Outcast - for me it's the best game of Star Wars,
- Planescape: Torment, best crpg in history,
- Medal of Honor: Allied Assault, another great fps,
If you like oldschool games with crappy graphics, you should try UFO: Enemy Unknown, there is a free port called OpenXcom. It's just like original but works with new operating systems.
So here you go. Maybe i forgot of something, but i loved all of these games.