[POLL] Best Single-Computer, Multi-Player, Party PC games

So I just recently set up a projector in the living room that's being used as a home theater running Win7 with XBMC, Boxee, MPC, VLC, etc.

I have a bunch of keyboards and USB joysticks and I would love to start running some fun, light party games on this big-a** new screen. The machine itself is not super impressive, just a dual core with 512MB video. So far I've got our classic SSB64, but I'm looking for some more games without getting a console.

Surely there's gotta be a bunch of good, fun, light party games for PC, right?