The Power Broker: Robert Moses and the Fall of New York by Robert A. Caro is a masterful book. It is really long (1162 pages) and very dense and took me over three months to read. but it is worth it.
I now have had a chance to read all four Caro books (three are on Lyndon Johnson) and they are four of the best biographies I have ever read. I hope and pray that Caro blesses us with another biography soon.