Billboard Liberation Front
Good read about the BLF I found linked at Fecal Face. It's an interview with the BLF's point man that tries to find some shared motivations between the BLF and graffiti writers. While the BLF won't get lumped in with any specific movement they at least don't pull rank which can always be annoying and sad, like when Dee Dee Ramone experimented with Hip Hop.
More Billboards at the BLF flickr page.