The Man in the High Castle by Philip K. Dick
First off, the obvious question - why did I read The Man in the High Castle. I don't WW2 books or, in general, sci-fi. A friend made me borrow it and he never suggests books, so I felt like I ought to read it. And then Michelle came up with her Sci-Fi Summer read-a-thon, so it was the prefect excuse. After all, according to the blurb, this is the book that established "Philip K. Dick as an innovator in science fiction."
On a side note, I never realized alternative history is a sub-genre of sci-fi. I tend to think of it more as fantasy. Wikipedia says, "since the 1950s, this type of fiction has, to a large extent, merged with science fiction tropes involving time travel between alternate histories, psychic awareness of the existence of one universe by the people in another, or time travel that results in history splitting into two or more timelines. Cross-time, time-splitting, and alternate history themes...