American Prometheus, the Triumph and Tragedy of J. Robert Oppenheimer, by Kai Bird and Martin J. Sherwin.

I wanted to check it out before the movie comes out, and I highly recommend it for a very in depth view of his life.

I also recently finished On the Origin of Time, by Thomas Hertog, which I also recommend. It's about Stephen Hawking's final ideas and theories, told by one of his closest proteges. There are some incredible ideas in this book that I had never heard of before, and I'm a cosmology nerd.