Do you like old maps? NYPL has an excellent digital archive of old maps of New York City. While you are there, be sure to check out the previously mentioned amazing photographs of 1930’s New York City.
Did you know you can take a look behind the scenes of the NYPL digital archive? Just like google, they have a lab where they research and develop new projects and features.
Finally, if you are a real map aficionado check out the always interesting Strange Maps blog. I highly recommend it.