The Art of Agile Development by James Shore & Shane Warden.
I've been working through this book for the last five or six weeks and have been loving it. Usually I do a deep skim read of most books -- the kind of reading you do in college where you need to get the gist of a book and some of the pearls -- but this one's grabbed me into an intense period of reading, reflecting, and re-reading parts.
Warden and Shore have written a fantastic work here. The book covers all aspects of Agile from planning to delivery, and each aspect is broken down into sensible sections. It reads like a series of great articles on very granular components of Agile such as Refactoring, 10-Minute Build, or Stand Up Meetings, but it's so well-written that all the articles mesh together perfectly leaving a smooth path through the book.
Each article (and that's my description, not theirs) lays out a specific practice or component of Agile, walks you through the benefits of it, details how that practice fits in the larger picture, shows you how to implement that practice, and discusses how to identify when you might need to implement or rework the practice. Each article is extremely well done and approaches its topic from a very pragmatic view. There are also cross-references to other practices elsewhere in the book that can help you solve related issues. Additionally, there are great references to other books, articles, and web posts.
Overall the book's just terrific. It's easy to read, it's pragmatic and practical, and it's thought-provoking. Art of Agile Development can be used by newcomers interested in moving into Agile practices, but it's also absolutely applicable to Agile pros looking to improve their own system. It certainly got me fired up with a number of ideas on how to improve our process even more. Perhaps that's the best endorsement of this book.