Exhibition at MET “Before Photoshop” ended on Sunday, but the “After Photoshop, Manipulated Photography on the Digital Age” is still running till 27th of May.
I saw both exhibition on Saturday and they were very interesting.
Entrance fee USD 25 at MET is only recommended, you can pay how much you want.
http://www.metmuseum.org/exhibitions/listings/2012/after-photoshop