The Boston Banksy; "FOLLOW YOUR DREAMS-CANCELLED", aka Chimney Sweep

A second Banksy, titled "NO LOITRIN", graced the brick wall of a building on Essex St. in Cambridge until it was painted over in 2010. The remaining Banksy is located in a parking lot in Chinatown, also on a street named Essex. I visited early on a Sunday morning when the lot was empty; otherwise it's impossible to get up close.

I saw it a few times when it was still pristine, but as you can see it's a popular spot.

NOTE: Sadly, this had been whitewashed by the time I went to check in late 2011/early 2012.