recent addition to the ESRB ratings list reveals an upcoming "Classic Rock" track pack for Rock Band for PS2, PS3, Wii and 360. The ESRB rated the expansion with a "Teen" rating for violence, swearing and drug use. Not that you'll see any of that stuff going on, you'll just be singing about it.
Example lyrics given by the ESRB reveal three of the track pack's songs: "The Joker" and "Take The Money And Run" by Steve Miller's Band and "Holiday In Cambodia" by Dead Kennedys. All of which have been previously released as DLC. Expect EA to announce the full track list, along with the track pack itself, within the next few weeks.