Maps at the New York Public Library
The New York Public Library’s Map Division has literally hundreds of thousands of maps and thousands of atlases in its vaults; hundreds of them are available online through the library’s Digital Gallery. Holdings include the Slaughter Collection of English maps, maps depicting the history of the U.S. and of New York in particular, and more. You could lose a lot of time sifting through them all. Thanks to peacay for the link.