I found this fantastic page just yesterday: University of Iowa libraries bookbinding models digital collection
It is a collection of examples of different types of bindings sorted by types and historical periods. The site contains numerous pictures og the bindings from different angles.
This makes it very easy to see the different techniques used in the binding of books.
The site show both bound books and the structures that are normaly cowered by the leather binding (the wooden boards and the thongs that attach the pages to these boards).
Especially the "medieval" and "monastic" sections are really interesting!