If you are going to visit New York City, you might as well take pictures of some of the most iconic sites and buildings in the city. NYC has good photo opportunities on literally every block! The canyons of buildings, harbor background , and city lights makes it photogenic at all angles. You can take both close-up shots and panoramic skylines of the city. And you can experiment with night photography, people portraits, nature(Central Park) framed architecture, timed shoots, and just about everything else.
There are many tours that you can take of NYC, but if you like shooting photos than just get out and do some walking. The above landmark map can help you plan a good route of photo subjects for both black & white and color photography. If you are visiting in the fall and winter than plan on shooting some black & white shoots.
Good reference sites to get you motivated are:
Timpaphotography - Shooting NYC Photos
Digital-photography-school.com - A Photographic Tour of New York
http://www.photographymonthly.com - Building Photography
http://www.digitalcameraworld.com - Building Photography
Flickr - NYC people photography
Also, when in New York City, don't forget to visit the camera stores which are some of the biggest in the World.