Christopher S sent a link to the New York Public Lib’ary site where there is something… amazing. This will require some time to digest. If you’re peeking at this post early; do not follow that link.
UPDATE: Great collection of mostly-stereograph, mostly-late 1800s photos. Unfortunately, the New York public lib’arians aren’t providing very high-res scans (at least considering what is left when you crop the frame and one ‘graph from a stereograph).