My friends and I just started playing Last Train Outta' Wormtown last night and it's a blast with a group. One player plays a worm who can only detect players while they are standing on the ground. The goal of the worm is to kill all the players before they can fix a train and escape.
We've also just started playing Gangbeasts which is also a lot of fun with a group. I'm sure most have seen this one by now though.