You may have never heard of TED (no, not The Energy Detective), but they have some amazing speakers. You can really get lost for a day just perusing their website and watching the presentations.
Two of my "sustainability all-stars" have spoken at some of their events and I highly recommend watching their talks.
Amory Lovins is chief scientist of Rocky Mountain Institute and has written many books, including: Natural Capitalism, Winning the Oil Endgame, and Small is Profitable.
They were both involved in The Natural Advantage of Nations.