Warzone 2100 is opensource build of the Pumpkin studios windows game. It is now under GPL and works cross platform. Event the soundtrack and films are distributable now.
http://wz2100.net/tags: games opengl opensource
Open Liero is an opensource version of Liero that runs of the resources from the old windows version but makes it cross platfrom.
http://open.liero.be/tags: games opensource
Information site on linux games, includes updates on latest versions and new games etc.
http://www.happypenguin.org/free opensource first person shooter based of the old Cube engine
http://assault.cubers.net/tags: fps games opensource
Open city is a 3d city simulator written in opengl and sdl using c++. Site contains a game programming tutorial based around the creation of the game.
http://www.opencity.info/tags: c++ games opengl opensource sdl
Wormux is a cross platform gpl came written in c++. It is basically a worms clone but looks pretty damn good and works well.
http://www.wormux.org/phpboost/news/news.phptags: c++ games opensource
Archived list of free and commercial games available on linux
http://gwos.org/doku.php/games:starttags: games opensource
Website of a nice man who makes some simple free opensource games. Nice example of c++ using sdl.
http://members.gamedev.net/alfith/tags: c++ games opensource sdl
website that contains links to free game content such as sounds, images and textures.
http://freegamearts.tuxfamily.org/