Anything by Primus, obviously, would be pretty fun. Specifically I'd like to see "Winona's (sp?) Big Brown Beaver" in the game - pretty fast, silly, fun for all instruments, and it shows some needed love to the bass. Plus, they were in GHII so I would expect to see something by them pop up in DLC (please!?). Dunno if censors would have an issue with the thinly veiled references in "Beaver", though...
Of course, more Red Hot Chili Peppers would be nice, but a song that I liked that I think would be pretty fun in the game would be "Aeroplane". Pretty catchy, fun to sing, nice guitar parts, and a really cool bass solo. Features a recurring F-bomb, though, but shouldn't be too hard to edit. Maybe they could even do some MoCap on Flea's daughter and make her run around on stage during the song! (Just kidding ;) If that doesn't make sense, go watch the video on YouTube - one of those kids is his daughter)
The challenge would be finding a good bass song that has really cool parts for the other members as well...









