Every Friday I take the initiative to search through thew newly free titles on Amazon, and to identify those that might be of interest to trans* readers, fans, and lovers. Even if you don't have a Kindle, you can still download the titles through one of Amazon's free reading applications, and covert it (if need be) with Calibre. I can tell you I do most of my reading on my iPad, using Kindle for iPad, and it works beautifully.
Please do be sure to check the price before downloading anything, though, as most freebies are limited time offers, and some are specific to certain regions.
Robin: A Genderqueer story.
Honeymoon Surprise (Futa Gender Swap 1)(gender swap, futa-on-female erotica) (Futa Honeymoon Surprise)
Summoning the Succubus
Mark of the Futanari 1: Party Girl's Surprise
SISTER, SPANKINGS, SISSY MAID, PART ONE (a sissy maid missy sister series Book 1)
THE BAD BOY THE SISSY MAID (a sissy maid missy bad boy series, part six Book 6)
Stranded on Futa Island: MFT Erotic Adventure
Maxwell: The Complete Series, 9 Books in 1 Gay Prison Erotica Bundle
Pledging Obedience (Pledging the Futa Sorority 1)(Futa-on-female, menage, voyeurism, college erotica)
Futa Teacher's Pets (Queen of the Futa Academy 1)(Futa-on-Female, Futa-on-Futa, Creamy, Menage, College Erotica) (Queen of Futa Academy)
The Shemale Trucker Erotic Tranny Story
The Shoggoth Secret - Lovecraftian Erotica