Have you tried out Frictional's free games, Fiend and Energetic?  They're pretty good, if short, it'll provide some fun for ya I'm sure, even for a little while.
Battle for Wesnoth I'd have to recommend, if you haven't tried it already.  It's a turn-based strategy game/RPG, and it's damn well-made.  Check it out!
http://www.wesnoth.org/
It's made by the Linux community (although Windows versions are available), and I must admit, it's one of the best free games I've ever played.  It might not look impressive with its simple sprites and animation, but the game play aspects are stupendous.