"By Its Cover: Modern American Book Cover Design" looks like a book I should already have on my bookshelf. I'm not super excited about the cover, but the book itself seems pretty awesome.
A pretty extensive preview of "By Its Cover" is available on Google Books, and Amazon has a few thorough reviews. I really enjoy how the book begins (keep in mind it was published in 2005):
"Is the printed book destined for eventual extinction? Is the thoughtfully designed book cover approaching obsolescence? The availability of ebooks has indeed increased, and print-on-demand technology will likely change the way books are marketed and purchased. But there is something special about the mass-produced book as an object—it is more than just a presentation of the ideas of an author. When a text is published and the book is designed and printed, it becomes a physical manifestation not just of the ideas of the author but of the cultural ideas and aesthetics of a distinct historical moment."