This doesn't address male-only photos, but there's nothing I find hotter than an air of anticipation in a couples photo, i.e., a situation where both the man and woman are clearly in a sexual situation--the applicable body parts either exposed or teasingly presented, the women with erect nipples, the guy with either a semi- or full erection--but there's no more graphic contact between the couple than maybe some groping. To me, that type of thing is the perfect balance between artsy and pornographic.