[Kyutetsuki]

"The left hand of darkness" by Ursula K. Leguin. A planet where the natives have evolved out of the ancestral humans that colonized it eons ago into androgynous creatures that only grow genitals when they "kemmer", essentially go into heat. They can flip between female and male several times in a lifetime. The novel is very much centered around what happens in a society where gender is that fluid. It's also sexualized several times in the story, and even more in two short stories set in the same world she wrote later - It's not really wank off material, but it's definately the most arousing "serious" TG work I've read.

Also, I can discuss it with my feminist friends without seeming like a pervert.