If you own both Guitar Hero (III or World Tour) and Rock Band (1 or 2), you'll be both familiar and ultimately sick of the compatibility issues between the two franchises. They will work, they won't work, they might work, they should work; trying to get hard, final word on just which instruments will work with which game has been a messy, convoluted and confusing experience. Until now, that is! The official Guitar Hero community crew have put together an extensive chart, outlining which instruments will work with which game. Bravo. Click through for all four charts for all four platforms.
Guitar Hero Instrument Compatibility Chart (locked) [Guitar Hero]