Very interesting topic...
There are a couple things that "come" to mind as my current favourite little kinks, one of which is a creampie fetish. It's an incredible turn on for me to clean up after I've made a bit of a mess. It's very difficult to do, as more often than not, my desire fades after orgasm. However, with an encouraging partner it's much easier. The times that it has happened have always been very erotic for both of us.