The New York city photo archive has over 800,000 images and you can spend a lot of time looking but here's a great story with some of the best:

http://www.theatlantic.com/infocus/2012/04/historic-photos-from-the-nyc-municipal-archives/100286/

To view the archives go here: http://www.nyc.gov/html/records/html/gallery/home.shtml

Enjoy