I've always loved Florence and the Renaissance. After my recent trip to the city, I've decided to update my library detailing its history.
April Blood: Florence and the Plot Against the Medici, by Lauro Martines
The House of Medici: Its Rise and Fall, by Christopher Hibbert
The Borgias and Their Enemies 1431-1519, by Christopher Hibbert
Florence: The Golden Age, 1138-1737, by Gene Brucker
April Blood is a particularly compelling read. Anyone who has played Assassin's Creed 2 should give April Blood a read, as it gives much of the background on the conspiracy against the Medici that forms much of the plot of the game.