Just some days ago, I updated my article Rare Type Specimens at the Open Library. In a comment, a user suggested another great resource: The Silver Buckle Press Collection.
Silver Buckle Press is a working museum of letterpress printing dedicated to preserving the craft of fine printing through educational programming, publications, exhibitions and tours. The Silver Buckle Press holdings of books, wood and metal type, hand presses, and printing equipment are part of the University of Wisconsin–Madison Libraries. And many of these books can be enjoyed online: http://digicoll.library.wisc.edu/SilverBuckle/Browse.html
Below are some personal picks. Just click on the image browse thru all the pages of each publication.