Here is a good place to buy Linux Games:
http://www.tuxgames.com/
They have quite a few like:
- Return to Castle Wolfenstein
- Kohan: Immortal Sovereigns
- Sid Miers:Alpha Centauri
- Rune
- SimCity 3000
- Heavy Metal: F.A.K.K.2
- Quake III Arena
- Unreal Tournament
- Tribes 2
- Postal Plus
- Soldier of Fortune
- Shogo: Mobile Armor Division
- Railroad Tycoon II: Gold Edition
- Myth II: Soulblighter
- Jagged Alliance II
- Heroes of Might and Magic III
- Civilization: Call to Power
I have bought quite a few from them...