David Allen is a productivity consultant and legendary expert in the field of human productivity. He is the author of "Getting Things Done", a time management guide, and a few other books on the same subject. His work is very easy to read and to follow, but this is not your everyday, afternoon-book-to-read piece. It's full of simple methods which you can learn and practice, and see the results very soon. He is the creator of the David Allen Company, whose presenters regularly give one-day public seminars on the methodology. Allen himself occasionally gives lectures or sessions. I've had an amazing time talking to him, I recommend you taking notes because this one is really helpful. Enjoy!