Checkout http://www.adbusters.org
This is what they say about themselves;
"We are a global network of artists, activists, writers, pranksters, students, educators and entrepreneurs who want to advance the new social activist movement of the information age. Our aim is to topple existing power structures and forge a major shift in the way we will live in the 21st century."
Amongst other things they produced a very powerful, amusing and artistic spoof corporate adverts.
Well worth a look.