Rock Band 2, standalone instruments coming next week

Harmonix has announced that the Xbox 360 version of Rock Band 2 has officially shipped to retailers in time for its September 14 release date. The standalone wireless drums and guitar are also shipping sometime next week for $90 and $70, respectively. Also shipping next week are Mad Catz's "Fender P-Bass" wireless guitar controller ($70) and the ION Drum Rocker set (wired; $300).

The press release also reminded us that the RB Music Store had recently surpassed 21 million song downloads since its launch in late November. That's 15 million more since we last heard about it in March and an average of 2.3 million per month.