Here's one, for example, that went into the Brooklyn Museum:

And this one adorned the walls of the Metroplitan:

Finally, for a link to the coverage of this art attack, go here to this amazingly great web site that covers "street art":
http://woostercollective.com/
As for Banksy, he had this to say about his raid on the art establishment (text of the interview found at the woostercollective site):
"These Galleries are just trophy cabinets for a handful of millionaires. The public never has any real say in what art they see. Its good to screw with the selection process sometimes. 'Comfort the disturbed, and disturb the comfortable' as Eleanor Roosevelt once said."