Knowing all that goes into the final design of a book cover (pleasing the author and agent, not to mention everyone here at Harper Perennial, can be an exhausting job for our amazing cover designers), this has become one of my favorite sites. It’s run by a graphic design firm, and every couple of days a new book cover is featured. Commenters (most of whom seem to be designers themselves) can then weigh in. I don’t claim to have any great design sensibility, so it’s always interesting to see where my opinions intersect with those of trained professionals. A cover can sell or sink a book, and this site has some insight into why.
They’ve covered some great Harper Perennial covers, of course: The Seven Days of Peter Crumb, The Gulag Archipelago, and The Dead Beat (a book about the somewhat wild world of obituary writing that I read recently and loved; any fan of Stiff or Spook would too), as well as many more.