Apparently available "this holiday" (Christmas 2008?), Guitar Hero 4 sounds like it is going to contain a number of the features that makes Rock Band interesting.
According to Eurogamer:
Activision has yet to confirm any of these features.
According to Eurogamer:
Eurogamer said:Guitar Hero 4 will reportedly include a set of drums, a bass guitar and microphone support and allow you to create and share your own songs.
Activision has yet to confirm any of these features.