I have been loving the work of Banksy for a real long time. He´s humorous in a really clever way and very political. I think his art is truly making a difference because it is so evidently incorporated into the cityscape and appears in places that you wouldn't normally see art and therefore catches the public off guard in their way out and about in the city. He will cheer you up on a dull day! Check out his website here for more examples of his amazing work.