When you complete the Final Band Challenge for RockBand 2 - you can get cool stuff at My Closet menu in the Rock Shop:

• Final Band Challenge on Bass
  • Silver Bass
• Final Band Challenge on Drums
  • Silver Drum Set
• Final Band Challenge on Guitar
  • Silver Fender American Deluxe Stratocaster HSS
• Final Band Challenge on Microphone
  • Silver Microphone