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
Horde 3d is a small opensource 3d engine with lots of fancy 3d features you would expect in a recent 3d engine. It is licensed under the Eclipse license
http://www.horde3d.org/tags: 3dengine c++ 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
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