I'm a huge fan of Orson Scott Card's Ender's Game series. If you find non-fiction books on leadership a little too dry, I think his are a nice fictional way to see how leaders can vary their styles based on individual personalities.
I'm not sure if this counts as a leadership book, but I just finished reading Here Comes Everyone, and I highly recommend it. (Thanks to another GovLoop member for loaning it to me!)
I think understanding social networking is going to be key in the future. This book gives several examples of how the internet/web has influenced the way groups form and communicate.