I'll add a little more info here soon, but for now, quick links to mailing lists:
Penultimate (MWF lunchtime game): Mailing list info page
usat (Tue evening / Sat morning game): Mailing list info page
Caltech Ultimate Disc Club (hasn't been updated in a while): Web site
Slackers Ultimate (Wednesday lunchtime game, not actually at Caltech): Mailing list info page