Image by The Book Cover Archive
You can find some really amazing book cover designs on this site. The Book Cover Archive is defined by its creators as serving the purpose of appreciation and categorization of excellence in book cover design - you can judge by yourself based on some of the examples from the site... It also provides an interesting section on portfolio sites of book cover designers and has a blog covering industry news, site updates, assorted book cover-related miscellany.
So the popular 'Don't judge a book by its cover' probably wouldn't work for the books mentioned on this site... would it?
Images by The Book Cover Archive