Footwear of the Middle Ages - http://www.personal.utulsa.edu/~marc-carlson/shoe/SHOEHOME.HTM
A meticulously researched site detailing information about all kinds of shoes and techniques from ancient times to the Renaissance. Essential for understanding the basics of cordwaining as well as all raised heels.
Elizabeth Bernhardt's Homepage - http://www.chass.utoronto.ca/~ebernhar/index.shtml
An interesting and useful website, giving broad historical information on Venetian chopines.
The Crispin Colloquy - http://www.thehcc.org
A discussion forum with some of the most educated and informed mind on all topics of shoemaking, including sources, history, references, and techniques.
World Catalog Libraries - http://www.worldcatlibraries.org
This is an excellent resource for finding all manner of books all over the world.
Arts and Sciences Homepage - http://www.pbm.com/~lindahl/arts_and_sciences.html
A superb resource for all things A&S. Specifically useful for finding transcriptions of manuscripts.
The Museum of Fine Arts in Boston - http://www.mfa.org
The website for the MFA, which has about fifteen pairs of chopines in its collection.
The Metropolitan Museum of Arts in New York - http://www.metmuseum.org
The website for the Met, which has a very nice example of a Venetian chopine. There is also a little article at http://www.metmuseum.org/toah/hd/chop/hd_chop.htm. Although the author, Harold Koda, doesn't give much detail on his references, his text does seem to jive well with the research that I've done.
The Bata Shoe Museum in Canada - http://www.allaboutshoes.ca/en/heights_of_fashion/east_meets_west/
The website for the Bata shoe museum in Canada, which has a very nice example of a Venetian chopine. Specifically, if you look to the right hand side of the window and click on the chopine that says "3D," then you can get a 3 dimensional look at this marvelous piece of work.
The Victoria and Albert Museum in Great Britain - http://www.vam.ac.uk/vastatic/microsites/1487_renaissance/intheround.html
The website for the V&A in Great Britain, which has a very nice example of an Italian chopine that is not quite so tall as the one in the Bata. This also has a 3D look, and you can see many of the same construction techniques.
Cervantes Virtual Library - http://www.cervantesvirtual.com
A great collection of Spanish documents online.
Google Books - http://www.google.com/books
Hard as it might be to believe, Google has digitized a wealth of knowledge, and all in text based searches.
The Leatherworking Reverend's Blog - http://leatherworkingreverend.wordpress.com/
The Leatherworking Reverend's Blog - an excellent resource for many leather-related articles, activities, and research. A lot of great stuff on leather bottels, costrels, shoes, pouches, etc.
Al Muckhart's Blog - http://wherearetheelves.net
An excellent source, penned by a fellow re-enactor, on shoes and shoemaking. A great resource for someone intereted in learning more about the process of both Medieval and Renaissance shoes.