The Municipal Archive has released 1,000,000 photos out of its huge collection and has posted them online. I have included the Gothamist link, because the archive site was down yesterday. But looking at the few in the Gothamist article, there is great stuff there. In particular, one of a builder in Brooklyn looking at Manhattan as he works on the Manhattan Bridge, and Lucky Luciano's mugshot. My favorite is the one shown, two girls walking east across 42nd Street in 1890.