It's difficult to choose a favorite when thinking about history books, as that genre makes up the overwhelming majority of my book reading. If I must narrow it down, though, I don't mind naming the following:
Doris Kearns Goodwin's Team of Rivals: The Political Genius of Abraham Lincoln. Miss Goodwin's book is a superb biography of Abraham Lincoln, but it is also a decent portrait of the time period and its major players. Also, despite the scope of her subject, the author keeps the writing accessible and thrilling, and has no shortage of intriguing quotations and anecdotes that make the biography and history as much of a page turner as your best mystery novel.
Jared Diamond's Guns, Germs, and Steel: The Fates of Human Societies. More than an eye-opening presentation of the argument that the rise of civilizations has nothing to do with race but everything to do with environment and location, Mr. Diamond's work is a portrait of humanity and his environment.
Walter Karp's The Politics of War: The Story of Twhttp://www.affiliateseeking.com/forums/newreply.php?do=newreply&noquote=1&p=17282o Wars Which Altered Forever the Political Life of the American Republic 1890-1920. Mr. Karp's is a controversial thesis that shines a different light on the major players of the time period between the lead-up to the Spanish-American War to the end of the Great War. I was particularly intrigued by his portrait of Woodrow Wilson, who he considered a treacherous and conniving figure worthy only of our scorn.
As for non-fiction, deciding on a favorite is much simpler! Frank Herbert's Dune has a special place in my heart because of how much it has inspired my imagination. The regality, religion, politics—every aspect of it urged me to read on.