It's one of myfavorite forms. You can definitely see the influence Fafi has had on my style. Although she has all kinds of deals now (like the one she had with nike) , she started as a street artist
It's hard to bring up graffiti without mentioning Banksy. Based in the UK, he uses stencils a lot. His works are very witty, and sometimes can be quite political. http://www.banksy.co.uk
(These images are quite big, I hope it's ok to post them? If not, just tell me and I'll take them off / link to them instead.)
One of my favorite collaboration projects- Chromopolis organized by the Carpe Diem and Greece to show Graffitti as an artform. They painted 10 cities up.
I'll put up the link to te pictures instead since they are big and plenty. I wish some of them had better pics...I'm trying to locate some detailed shots.