Local Multiplayer PC Games?

This weekend I'm traveling out of town to visit some old friends I haven't seen in awhile, we plan to spend the whole weekend hanging out and drinking booze, and I'd like to enliven to event with some cool couch MP games for my PC. I've already got Nidhogg and Samurai Gunn lined up, I was thinking of getting Risk of Rain too. Are there any other cool 2-4 player local co op games I can get on my PC that are easy to pick up and play without too much fuss?

If you want to play something with a bit of longevity you can never go wrong with some Trine 2.

I've got trine 2, that's a good game, but I think we might not have the brainpower for that after a short time

Divekick. And the pre-alpha build for Gang Beasts (if you haven't already watched the 02/14/2012 UPF, you should. Jump ahead to about 1:28:00 to see Gang Beasts in action).