Why hasn't anyone mentioned Doom 1 or 2? Wolfenstein3D?
great games!!! How about some older Half Life games? Like Blue Shift Or Opposing force. I bought mine both in a pack at best buy for $9.99
Oh yeah, and don't forget Rainbox six. Civilizations: Call to Power, This old really good RPG game called "Shannara", Disciples. Running out of ideas.....