For the first week, you will be able to get the new Soundgarden album, Telephantasm for free when you purchase Guitar Hero: Warriors of Rock. In fact, since the album does not officially get released until October 5, you will be getting it a week early!
Also, starting on the September 28, you will be able to download (not for free however), the entire album to play in the game (we are assuming this is only for Warriors of Rock and not for Guitar Hero 5 or Band Hero).