The New York City Department of Records has put a huge portion of the Municipal Archive’s collection of photos online, more than 870,000 in all. The server is overwhelmed at times due to heavy usage, the searching/browsing interface is not what you’d call cutting edge, and many of the photos are available in thumbnail size only, but this is still an incredible resource.
Painters on the Brooklyn Bridge in 1914:
The unfinished Manhattan Bridge in 1908:
A pair of men lay dead in an elevator shaft after a failed robbery attempt:
Looking east on 42nd Street, circa 1890:
More of these photos can be seen at The Daily Mail. (thx, miro)