Build and Shoot

Basicallyy, Star Trek. Six-player co-op Star Trek. I'm not a trekkie myself but this is still ridiculously fun. Probably most of you won't be able to get the people together (it's much better in person than over the internet imo), but even just two or three can be awesome.

Anyway, take a look.. I don't think videos do it justice, but there are plenty on youtube and the demo's free.

Artemis

I've heard of it. Looks cool.