Two weeks ago, The New York Times hosted an Exhibition named "Killed Covers"(they are all rejected book jacket, however, they are still awesome), here is the link for those people who don't live in NYC.
http://www.nytimes.com/interactive/2011/05/15/books/review/15covers-gallery.html
(Pic above: Design by Christopher Brand: "Heft")
(Design by: Will Staehle: "Manhood for Amateurs")