I just set up a Big Cartel page for my band about three days ago, so far it's working out quite well:
7horns7eyes.bigcartel.com
If you want your stuff on iTunes I'm sure there are many inroads, but I know that you have to be "represented" by some kind of company, as iTunes doesn't work directly with artists. My band went through CDbaby after getting our CDs manufactured with Disc Makers. I think it's like one $35 setup fee with CDbaby to get your mp3s submitted to all of the main companies- iTunes, Napster, Rhapsody, Last.fm, Amazon, and plenty of companies I hadn't previously heard of. My band is out there on 25 companies...you can even buy our cell phone ringers directly from Verizon, haha. I'm sure that on the grand spectrum of things, what we're doing is relatively small, but it's cool nonetheless!