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.
Sci-Fi Gender Bender Bundle 2
In Her Clothes
The Futa's Pet Slave (Dominant Futa on Submissive Male)
Tutor Nari's Secret (A Futa on Female Romance) (Tutor Nari's Girl Book 1)
Gift of the Futanari Goddess Pt. 3
The Pink Vial: A Gender Swap Fantasy Short Story
The Moonshawl: A Wraeththu Mythos Novel