The Medici: Godfathers of the Renaissance by Paul Strathern.
^^Such a very good book - and they made it into an equally interesting documentary that aired on PBS a few years back.
Fire in the City: Savonarola and the Struggle for the Soul of Renaissance Florence (Lauro Martines)
American Prometheus: The Triumph and Tragedy of J. Robert Oppenheimer (Kai Bird & Martin J. Sherwin)
I'm not normally a fan of biographies, because I've been forced through some incredibly dull ones, but these two are especially good, I think.