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.
All Dolled Up 2: The Crossdressing Chronicles
Taken By The Succubus (Futanari, Paranormal Erotica)
Vampire: Taken by the Futanari Witch (Paranormal Erotica)
Taken by the Futa Cougar (Paranormal Futa Erotica) (Taken by the Paranormal Futa Book 1)
The Witch Who Stole My Manhood (Gender Change, Futanari Erotica)
My Naughty Roommate: The Futanari Succubus: (Erotica)
Gender Swap Bachelor
Don't Drink and Gender Swap (Gender Change, Transformation, Erotica)