Toribash (ragdoll game, where you control the character by moving his joints and fight with other players/dummies)
Battle for wesnoth (a turn-based strategy game with fantasy theme, cool units and leveling, lots of maps and editor and really good campaigns.)
OpenLieroX (Kinda like 2-D worms, but real-time instead of turn-based)
Trackmania Nations forever (a driving game where you can build your own tracks. nice graphics.)
Soldat (2-D shooter game. A bit like liero, but more realistic and better graphics.)
i played all of these.
/recommend