Rock Band 3

Cheats:

Unlock the Ovation D-2010 guitar:
Using the guitar, press Orange, Blue, Orange, Orange, Blue, Blue, Orange, Blue at the main menu.

Unlock the Stop! guitar:
Using the guitar, press Orange, Orange, Blue, Blue, Orange, Blue, Blue, Orange at the main menu.

Unlock the Guild X-79 guitar:
Using the guitar, press Blue, Orange, Orange, Blue, Orange, Orange, Blue, Blue at the main menu.