This is pretty amazing: Property Shark has added pictures of every building in Manhattan to their maps page. Instructions via their press release:

To find photos using our map, go to our maps, click on Manhattan and then keep clicking. Each time you click, you'll zoom in. Then, when you get to the lowest zoom level and can't zoom any more, if you click on a building you'll bring up the photo of the building along with a description. Click around some more to see other buildings.

There have been other efforts to comprehensively map every building in the city. In 1939, the city's tax assessors did a complete set-- these can be purchased from the city or viewed on microfilm, but sadly are not yet available online. Frank Didik tried to assemble a similar archive in 2002, and most of those pictures are up on his site. Then there is Amazon's A9 maps, which includes street level pictures for major streets and avenues, but lacks images for most of the residential areas of Manhattan. And of course, nothing like this is available yet for the outer boroughs!