Team of Rivals: The Political Genius of Abraham Lincoln, by Doris Kearns Goodwin. I've always been fascinated by Lincoln, and this is a very good (and long) biography. It has a twist though. Instead of just recounting facts about and events in Lincoln's life, it compares and contrasts Lincoln with his three Republican competitors for the presidency in 1860: William Seward, Salmon P. Chase, and Edward Bates. I didn't know anything about those guys. I'm learning a lot about Lincoln's political maneuvering, ideology, character, and approach to leadership in the context of the 1860 election. I find two things particularly fascinating: One, a relatively unknown Lincoln captured the Republican nomination and the presidency from men much better known and more experienced than he; and two, he brought his three rivals on board his administration, rather than distancing himself from them. That takes a lot of guts and humility.
Not to mention I am also getting a better understanding of the way slavery was viewed by the different political parties and factions of Lincoln's day.