Here’s a list from io9 of books (many are actually fantasy) that have science fiction themes and what they consider “kinky” sexuality. They are all humanoid, or at least one of the participants is human or humanoid. But most of them are fun and or provocative reads, especially Lilith’s Brood (formerly known as Xenogenesis series) by Octavia Butler and Extraterrestrial Sex Fetish by Supervert.
Buxom and fierce Boris Vallejo cover for The High Couch of Silistra
Great blog featuring hundreds of aliens from popular culture. Many are humanoid, of course, but there are loads of non-humanoid aliens to peruse with images and descriptions. Unfortunately I haven’t found any discussions of sexuality here. Does that mean that aliens are not interested in sexual pleasure and/or sexual reproduction? I hope not.
Here’s and image of a Bringer of Wonder from Space:1999