We should be listing here books where the sexual aspects come from the content and not from the picture used to represent the book (so please try to avoid covers depicting explicit kisses and/or touches, naked or half-covered bodies clearly designed to express a sexual characteristic of the protagonists, or any other element meant to imply intimate aspects of the relationship).
Let's appreciate the covers by the effort, creativity or inspiration of the artists, and not by the hotness of the male models!