Games I play: Nexuiz, 0 AD, Freeciv, FreeOrion, SuperTuxKart. If you want something Quake-like, Nexuiz is probably your best bet in the repos.
0 AD is something of a cross between Rise of Nations and Total War, while Freeciv is a Civ II clone and FreeOrion a Galactic Civilisations clone. SuperTuxKart is a racing game with similar mechanics to Mario Kart. My favourite games in the non-free world (before I left it) were Fallout 2 and Morrowind.
