A fun, small little game that I found:

http://sauerbraten.org/

I'm having a lot of fun in it, anyway. iCTF is the most-played mode by far, so if you're a fan of iCTF or would simply like a fun, simple (compared to Quake, at least) game, I'd say give it a go. 100% free, nothing to lose. :)

Not to mention ping has hardly any affect on the game whatsoever -- you often see people from all over the world fragging merrily in one server. ;)

Community isn't terribly large, but I never have trouble finding a populated server, or a handful of populated servers. Wonderful little community to boot.