I just played Xonotic for the first time ever and now I'm interested. I like a game I can be sure isn't selling my data to China.
I would personally like an RTS, a game in whatever genre Stick Fight falls under, and sandboxes, although any genre is fine. I don't contribute code, but I'm pretty good at finding bugs, etc. and get a few laughs out of people on the forums with my jokes.
Games in early development preferable, mostly for the active community these tend to have, so I can share less formal work with them and join their Matrix.org room or something
Liero - a real time version of Worms
Scorched 3D - Full 3D version of Scorched Earth with fully destructible terrain
Vega Strike - open world space flight sim
Soldat - 2D shooter based on the Quake 1 source code. Now on Steam
Cataclysm: Dark Days Ahead - turn based post apocalyptic roguelike
Warsow - FPS, based off of the Quake 2 Engine
WG Realms 2 - glorious mashup of Doom and Duke3D