Here are a couple favorites of mine:
The Arabesk trilogy by Jon Courtenay Grimwood--
Pashazade,
Effendi, and
Felaheen. Alternate history of a slightly different sort, which takes place in a 21st Century where the Ottoman Empire never fell.
Amazon Kindle link:
http://www.amazon.com/Pashazade-Arab.../dp/B000FCJZHM
And a classic, which may not be available as an ebook:
For Want Of A Nail: If Burgoyne Had Won At Saratoga, by Robert Sobel, which posits a world where the American Revolution failed and the revolutionaries emigrated to Mexico. It reads like a history textbook, complete with footnotes and (fake) references.
Amazon link:
http://www.amazon.com/For-Want-Nail-.../dp/1853675040