Guitar Hero: World Tour before New Year's Eve. It only applies to the "Complete Guitar Game" variety that retails for $99.99, which is the package that comes with the game and a guitar controller, but not the standalone game or the more expensive "Full Band Kit". DLC is usually about $2 a pop, so you'll be saving about $10 with this deal. Of course, if you own the game already, this simply means you are getting 5 songs for free.
Some people will try to compare this deal with the 20-song DLC Rock Band 2 offered a while back, but in this case you actually get to pick and choose which songs you want.