Ah, 3 games I left out:
* Naev (the one I couldn't remember the name of) 2d-space combat
and trading game
* Openttd- opensource extension of microprose's transport tycoon
deluxe. Recently 100% free, no longer requiring buying
the original game. http://www.openttd.org/en/
* Warsow - FPS http://www.warsow.net/