Other Book Design Sites
Publishers' Bindings Online -- a very large site covering the period from 1815 to 1930. Very easy to search, by author, designer, and all sorts of keywords (find covers with birds, or mountains, or Hats, for example, or blue covers!).
Beauty for Commerce: Publishers' Bindings, 1830-1910 - Organized by the Rare Books Division of the University of Rochester Libraries, it is arranged by decade, with special sections on Margaret Armstrong and Sarah Wyman Whitman.