talking of graffiti...

I've been aware of Bristol graffiti artist and stenciller Banksy for about eight years now, having spotted his work around Manchester on numerous occassions.
If you haven't already, and you're into clever, guerilla art he is well worth checking out. His intelligent - and often highly political - pieces have popped up across the world - including on the wall the Israelis are building to keep the Palestinians out:

and

He is now becoming quite mainstream, and has had exhibitions in galleries, but hasn't lost much of his edge and remains extremely secretive about his identity and fiercely opinionated. When asked on his website whether graffiti is art or vandalism, he says: "That word has a lot of negative connotations and it alienates people, so no, I don't like to use the word 'art' at all."