This well-written and easily digestible book by Dave Pelz is as good as any book you're likely to encounter on the subject of putting. It teaches all the fundamentals and backs them up with Pelz's research.
One of the most useful parts of the book is the putting games that it describes. The most useful of them, "Safety Drawback," teaches you to hit the ball into a "cone" past the hole.
Reading this book alone won't make you a better putter, of course. That'll take about 10,000 more practice putts. :) But at least you'll know what to practice.
I can't find any major faults with this book. Pelz suggests a particular technique but he also accepts that many other strokes and techniques work well. Whether you're a beginner who is still trying to figure out what a decent putting stroke looks like, or an experienced player who is just trying to work out the kinks in his game, you'll find at least something in this book to help you. Highly recommended and, at present, there's no better book on the market as far as I know.