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
Planet Pinker (Transgender Guide to the Universe Book 3)
Up on the Stage (crossdressing, forced feminization)
Mother's Secret Sissy Son (Mother's Secret... Book 2)
My Futa-Loving Girlfriend (Futanari Massage 5)(futa-on-female menage erotica)
Futanari Dessert (Futa on Female Erotica)
A Dominatrix's Diary: Back to School (Femdom BDSM Humiliation Erotica)
The Lion Who Switched In My Wardrobe: (Forced Feminization, Reluctant Gender Transformation, Gender Bending)
Big Night Stick (Feminization, MFM, Gender Swap)
Gift of the Futanari Goddess Pt. 1 (Taboo Erotica)