$20 Off Portal 2 ($9.99)
Platforms: Xbox 360 / PlayStation 3
You're pretty smart, right? At least you like to think so. Portal 2 is one of the most clever - not to mention funniest - puzzle games to be released this side of the millenium. You owe it to yourself to have this in your collection permanently. Also note, if you get the PlayStation 3 version, it's cross-compatable with PC via Steam and includes a code to download an additional copy for your computer in the box!