The books available are Vol'jin: Shadows of the Horde, Rise of the Horde , War of the Ancients: The Well of Eternity, Lord of the Clans, Day of the Dragon, Thrall: Twilight of the Aspects, War of the Ancients: The Sundering, Wolfheart, and Night of the Dragon. You can learn more and look inside each book by checking out the deal page.
Don't have a Kindle? Don't worry, Kindle apps are also available for Android, iOS, Windows Phone and for PC and Mac computers. The app works almost as well as the Kindle itself, and has the advantage that you don't have to buy a device, and it's completely free. I would suggest that, before you go investing in the books, you just test the Kindle app with one of the many free books available for download. It's never been a problem for me, but better safe than sorry.
It's a great way to get your hands on some very reasonably priced Warcraft lore, but don't wait too long, it's only for today, December 17th.
[Thanks to the various readers for the tips]