http://www.loc.gov/library/libarch-digital.html – Library of Congress, best way to browse is by topic here http://www.loc.gov/topics/ – (Note: stuff that is not allowed to see in high resolution can often be found by name in a Google image search at much better quality.)
This from Columbia University is great for the typography use in the headers. http://biggert.cul.columbia.edu/items – They have other stuff but it is hard to find much that is useful for graphic design http://library.columbia.edu/digital/collections.html
This one http://quod.lib.umich.edu/cgi/t/text...rowse&c=genpub – has a lot of old scanned literature but not really much of a way to just browse.
Another University collection – https://www.lib.umn.edu/special
NY public library – http://digitalgallery.nypl.org/nypld…cfm?topic=all
There is this one as well focused more on architectural renderings obviously. http://www.architecture.com/LibraryD...llections.aspx
Another architecture focused one http://www.archivision.com/cgi-bin/a...i?isindex=base – alot of these are just photographs of buildings, but there are some drawings and the architectural detail stuff like the “Decorative Elements” is very good for reference if you need to draw some of that kind of stuff.
Then there is one of my all time favorites , the Dave Rumsey Collections http://www.davidrumsey.com/collections/ – If you like vintage maps their cartography is the best resource I know of, and the resolutions of much of the stuff here is amazing.
Other cartography stuff if you like