NYPL Digital Gallery

"The New York Public Library provides access to over 275,000 images digitized from primary sources and printed rarities in the collections of The New York Public Library, including illuminated manuscripts, historical maps, vintage posters, rare prints and photographs, illustrated books, printed ephemera, and more."

Once you see the site, don't make any plans for a few hours, as the array of choices is stunning.

NYPL Digital Gallery