Well, it was sort of leaked a couple of weeks ago (nice one, spraynwipe!), but it's now been officially confirmed - brand fusion has occurred again, this time with LEGO meeting Rock Band:
Players will become rockers as they embark on a journey to stardom that the whole family can enjoy as they work their way through local venues, stadiums and fantasy locations on Earth and beyond that mimic the imaginative settings that the LEGO world offers. Also continuing the LEGO ďbuild-and-playĒ gaming experience, players will be able to create their own LEGO Rock Band style as they customize their minifigure avatars, band and entourage, including roadies, managers and crew. LEGO Rock Band supports Rock Band instruments, as well as other music game controllers.
The press release
has some more information, including a couple of the included songs (notably, Europe - The Final Countdown... COME ON!).
More information and some screenshots are available on our LEGO Rock Band game page