I have some books to recommend. I learned of each of these books (except for the Ellis book) on this site.
By far the most important book I can recommend is The Feeling Good Handbook by David D. Burns. It is a true tour de force despite its sappy title. It should more properly be titled Workbook rather than Handbook. The book works only if you complete the exercises within 30 days after starting the book. It will teach you to face your demons and overcome them. Just like GTD. This has had more impact on my life in this last year than anything else.
Jinny S. Ditzler's Your Best Year Yet provides a nice organizational structure for creating year-long goals. I have done goal-setting before. But I found her structure to be just what I needed. I used this book to set goals for the June '04 through May '05 year. It was a useful exercise.
Smart Choices by Hammond, Keeney, and Raiffa is a layperson's guide to doing cost-benefit analysis. Cost-benefit analyses conflict with my deep-rooted humanistic tendencies but they do have their place. This is an important book for helping me structure important decisions. I just read it in the last week, so it has not had any signficant impact yet on my life. But it is clearly an important tool for my toolbox. I do intend to start using it.
Self-Help Without the Hype by Robert Epstein is out of print. I just finished it this week as well. It takes about an hour to read. I learned nothing new from it. It presents psychological behaviorism in a novelistic form, where the main character has weekly meetings with a fictionalized version of BF Skinner. Despite learning nothing new from it, this book gave me a well-needed kick in the butt to use behavioristic techniques to eliminate a bad habit. The actual technique I decided to use was placing side bets, an idea I got from Albert Elllis's Overcoming Procrastination.
Epstein reiterates the point that we each must find our own path. I do feel that GTD has a place in the pantheon of innovations right next to the invenstion of Arabic numerals. It is that important. But we all know that some people are just naturally organized and productive and don't like GTD. Others are disorganized and unproductive and don't like GTD. So we must each find what works for us. Epstein is a hard advocate for behavioristic techniques. But he stresses in his book that he will not tell us which particular behavioristic technique we must use. We will each learn this for ourselves by failing with some techniques and succeeding with others.
I have read a good number of the books mentioned by others already in this thread. To be perfectly honest, many of those books just were not useful for me. But I would never attempt to minimize the impact these books have had on others.
Lastly, I suggest that those who are interested explore
www.emofree.com . It is free and it may be of some use. I have found it to be inconsistent and yet, nonetheless, to be breathtakingly powerful at times.
