I just came across this Google spreadsheet of artists using Twitter. As with many major artist MySpace pages or blogs, the "big" ones are more likely label interns—or impostors with entirely too much time on their hands—than actual artists, but there's a good chance that a bunch of the smaller acts are actually speaking tweeting for themselves.

I've carefully combed the list and here are a few favorites...
Chris Cornell, formerly the lead singer of Soundgarden. Guessing it's fake but if it really is him... wow.

Mike Doughty, formerly of Soul Coughing. Pretty sure Mike is the man behind the tweets.

Sonic Youth. Not sure what's going on here. Thurston, is that really you?

MC Hammer which, since he owns a tech company here in Silicon Valley, may very well be the one and only Hammer. Or maybe his iconic baggy pants are doing the tweeting. Either way, I'm genuinely disappointed that his username isn't Hammer Time.