Rock Band 2 is coming out exclusively to Xbox 360 this September! This personally really excites me, to know that its coming out around the same time as Guitar Hero. I really like the notecharts of Rock Band alot more than Guitar Heros. Apparently the downloadable content will carry over as well. Which means I won't have to re-buy Jukebox Hero. Heh.
Also, its compatible with the old instruments, yay! "More variety of instrument choices than ever before with new and improved drum and guitar peripherals, enhanced functionality and innovative new designs - all fully compatible with the original Rock Band instruments."