Dirt 2, Codemaster's stunning rally racer, is only $5. Get on that now. Alien Vs Predator is going for just $6.80. Got a spare $2.50? Of course you have - go get Monkey Island 2 SE: LeChuck's Revenge.
Star Wars: Knights of the Old Republic is also $2.50, which is insane for the admittedly aging but still incredible RPG. Mafia 2's cheap as well.