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.
Futanari Sorority 1: Pledge's Initiation
Mother's Secret Sissy Son (Mother's Secret... Book 2)
My Futa Massage Parlor (Futanari Massage 6)(futa-on-female menage erotica)
Erotic Futagirl Bundle
The Sissy Within: A Submissive Sissy For The Futa Dom
What the Futanari?
From Cop To Cutie (Forced Feminization Femdom Erotica)
Alien Bite Gender Swap Threesome: Erotic Short Story
Gender Clones 3: Female Recall (Science Fiction Body Swap)
MEMOIRS OF A TRANSSEXUAL CALL GIRL: Enter the Butterfly
Her Name is James