I just finished reading Marcus Buckingham and Donald O. Clifton's book, "Now, Discover Your Strengths."
As the title implies, the book seeks to help you identify your strengths and then spends some time discussing how you can capitalize on those strengths. It even has an online assessment you can take to identify your top 5 strengths (you need to enter a unique code that is printed on the book jacket to register for the assessment).
All of this sounds really cool but, I must say, the book and quiz really left me wanting more. There was nothing revolutionary here for me - perhaps because I've read lots of books of this ilk, and I found this one to be rather basic compared to others I've read.
The analysis of my strength areas seemed fairly on target (in their terms, my strengths are Intellection, Learner, Connectedness, Ideation, and Input). However, I didn't get a lot of substantive information on how to develop those strengths, what kinds of people I should associate with to counterbalance my strengths, or anything like that.
The book also contained a fair amount of material on how to use this method as an organizational development tool. With good faciliation, that might be helpful since it would provide a way to play to the various strengths within the team (though I have been through some great team workshops with other tools).
In summary, I felt this book was a good introductory-level book, and if you're just getting into self-analysis and self-improvement, it could be very useful.
If, on the other hand, you've had experience with things like the Myers-Briggs Type Indicator test, the Keirsey Temperament Sorter, the Birkman Method, or other tools like them, you may not find a lot of additional learning in this book.
By the way - the tools I mention above are not free, and generally require a paid facilitator. If you're just dabbling, you can get a good (free) approximation of them by taking HumanMetrics' free Jung Typology test. Then, you can read more about the various types online or in the books Please Understand Me II, or Type Talk at Work.