In another thread there were some comments made about GPL games, so I thought I'd pull up a list of Open Source / GPL / Free games and boy is there is an interesting list on Wikipedia, so I thought I'd share :)
Enjoy!
Open Source Games:
http://en.wikipedia.org/wiki/List_of_open_source_games
Freely Downloadable Games List:
http://en.wikipedia.org/wiki/Freely_downloadable_game_software
Freeware:
http://en.wikipedia.org/wiki/List_of_freeware_games