WARNING: new and disturbing worlds follow.
Some Discworld fan has written Rincewind/Greebo slash. We can but hope that Greebo's in human form.
Also mentioned: Death/Librarian (the librarian is an orangutan), Vimes/Vetinari ("…one of the fandom's primary exports!") Death/Vetinari ("It's very Victorian and almost in-character.") and, not least, Rincewind/Luggage. See also.
‘Also, the image of Agent Smith slithering up and down Patrick Stewart's body, snake-style, is one that will haunt us until the end of our days, thanks so much.’