We've just kicked off the beta for the Rock Band Dashboard, and app on our official Facebook page! Check it out here: http://apps.facebook.com/rockbanddashboard/
The RB Dashboard is a cool way for you to explore the RB library (like a more accessible version of our Songs page) and let us know which bands you want to see in the game! We've been pointing people to RockBand.com/request for song suggestions, but the RB Dashboard offers a few different wishlists that are visible to everyone in the community, so you can see in real time which bands are the most requested.
So head on over there, get registered and tell us which bands are in your DLC wishlist!
EDIT FROM HMXcj: We just released an update to the app that includes a new stat called Skill Level. Check out the details and give us your feedback in this thread: http://www.rockband.com/forums/showthread.php?t=228226
NEW EDIT FROM HMXcj (4/3/12): We just released a new update to the app! Now you can compare your Rock Band 3 scores and skills to your Facebook friends and people you look up by Console ID. You can compare DLC libraries to see who you should play with. We'll even suggest new friends for you based on your similarities in DLC! (Note: This feature is still gathering data. You may not see suggested friends for the next 24 hours.) Let us know what you think!