Where can I view really artistic graffiti in the 5 boroughs of New York?

Im planning on doing some urban exploration this coming year and on the list of things I would like to see in NYC is very artistic graffiti. So I need to know where to find some that maybe I don't know about. I got all the musical ones ie Biggie Run DMC Joe Strummer Kiss and theres the one close to Queensboro. Now I need others perhaps in brooklyn but wherever. The bigger the better, the more impressive the better.