Although I am sure you are asking about ebooks, I want to recommend a pbook that I would classify as the most interesting history/biography I have read (I'm still in the midst of reading it
) in years:
Abraham Lincoln: A Life by Michael Burlingame. This is not for either the faint of heart or the faint of pocketbook -- it's 2 volumes (approx 2000 pages), hardcover, and costs $125 at full price (available for less at a bookstore near you). I am amazed at what there is yet to learn about Lincoln.
(One thing I learned in yesterday's reading is that Lincoln's law office was noted for being filthy. It was a second-floor office but hadn't been cleaned in so long that plants were literally growing from seed on the floor.)
An interesting history ebook is
Warriors of God by James Reston, Jr. It is the story of battle between Richard the Lionheart and Saladin for control of the Holy Land during the First Crusade.