Borderlands for the PC is a little further away than the 360 and PS3 versions of next week (OMG NEXT WEEK!), but that gives you plenty of time to organize a group of four people for this co-op deal Steam is offering.
You can pre-purchase a four pack of Borderlands for only $135, basically getting one copy of the game for free. In the end that comes down to $33.75 a person for some co-op gaming goodness. Yes please!
Of course if you are still on the fence for the game, perhaps the game's TV spot will sway you over the proverbial fence and into the Borderlands.