If you're in Chicago, there's a great event this Saturday and Sunday down in the Little Village area called Meeting of Styles, which is a group of graffiti artists who have had some buildings donated to them on which to practice their craft.
It's neat because these are really talented artists, but their craft is considered illegal, so they usually have to practice their craft in the dead of night. Here though, they have these buildings set aside for them so they can paint in the open, and let others of their trade see their work as well. Graffiti artists come from all over the world to tag and to view other tagger's work. Here's a link with more info about the event:
http://wallstreetmeeting.de/ And here's my pics on Flickr I took last year....it's a great place to take pictures. Check it out if you possible can.
http://www.flickr.com/photos/bodhisattva811/sets/72157622288978103/