Having just come across a publisher I'd not heard of before, I was really impressed by their cover designs. The publisher is Bookkake, and their specialty is saucy stuff, old and new, as well as a fascinating blog.
Here are the covers of their books so far (and any publisher who brings Hazlitt's fascinating, mad book of obsessive love back into print deserves applause). Each uses a simple, bold image of a body part (usually human) in extreme close-up. Click for much bigger versions.