Was listening to my iPod when I heard a few keyboard friendly songs that I think would probably work, though I know there's just no way in hell Harmonix would consider them. No, this is not a wishlist...just thinking a little outside the box.
It's Time To Party by Andrew W.K. - Good fast, stupid, party song. Only 1:30, though.
Lovefool by The Cardigans - I know, I know, but c'mon...it'd be funny as hell.
Lose Yourself by Eminem - Might be a bit too repetitive, and it loses like 1,000,000 points for being so ridiculously overplayed. But it would totally work
OK, and one that has a legitimate shot to be DLC at some point (since Spinning Wheel is already confirmed)
Lucretia MacEvil by Blood, Sweat & Tears - This would be ridiculously fun to sing if you try to emulate David's voice: Ooooooohhhhh Lucy you just so damn bad.