This deal has ended.
Possibly for today only, Newegg has Rock Band 2 for the XBox 360 on sale for only $14.99, despite its original $60 price point. Note that this is only the game and does not include the instrument controllers. Shipping is free and there is no sales tax (except CA, TN, NJ). They also have the PS3 and Wii versions for $19.99 each.