Quick shameless plug for one of my favorite games. If you've got a couple of friends who can play local and want a good co-operative platform/adventure/puzzle game, don't pass this one up. You will need a couple controllers, but I know Trine 1 is well worth the effort to play, and Trine 2 looks to be even better.
Trine 2 is 50% off this weekend on Steam, bringing it's price down to 7.50 for the regular or only 12.50 for collectors. The first Trine is 80% off, or a measly 2.00. Both are well worth the full price and basically a steal at this price.
Both games are very good 3 player local puzzle/action/platformers, with an emphasis on creative use of physics and the character's different powers. Both are also MAC compatible, for you MAC gamers out there.
I haven't had the time to write up a review of them on here yet, but the first Trine is good clean fun, and from the looks of it, the second one continues the tradition. Good clean fun for 1-3 players at once.