unreal tournament 2004
medal of honor : allied assault
call of duty
call of duty : united offensive
half life : source
Hlds and source games can be installed via steam, like posted above.
Search google for the other games, something like:
unreal 2004 linux dedicated server
mohaa linux dedicated server
Add directory listing to the search to find sites that list them, that way you dont have to register to download or download to your local pc and upload to a server.
Unreal comes in a zip, the rest come in .run files [besides hlds]