If you haven't switched to an agile approach to software development yet, you probably should. But be warned. Agile is not about daily stand ups in the morning. It also isn't about renaming your "work break down structure" into "backlog". Going agile requires changes deep in the internals of your team and/or in your company, depending on the level on which you want to go agile. In my experience there is just no reasonable way to gain the required understanding of agile approaches from on-line resources alone. I recommend the following three books instead:

Agile Software Development with Scrum by Ken Schwaber: Obviously this book is about Scrum, which is just one of many agile processes. But even if you don't want to go with Scrum, this book will teach you a lot about why Scrum is designed the way it is, and this will be very helpful, no matter what approach you choose. Be warned: the book is small, has crappy graphics and is rather expensive. But it is worth it's money.

Lean Software Development: An Agile Toolkit by Mary and Tom Poppendieck: This book isn't tied to any specific process or approach, instead it describes the underlying concepts, which are common to all agile approaches. And these are the ones that really count. Since the Poppendieck have a lot of experience in non software projects they provide lots of examples an cross references which might help convince a stubborn manager, who doesn't realizes that doing waterfall software development might be 10years behind standards in software development, but is about 50 years behind when compared with other branches of industry.

Management 3.0: Leading Agile Developers, Developing Agile Leaders by Jurgen Appelo: Unfortunately you can't buy the book yet. But I had the honor to review an early version of the book and provide Jurgen with my nit-picky comments. This book is very different from the other two, because it focuses completely on the management side of things. Agile doesn't mean managers will go away, they don't even become useless. Quite the different, they might actually put themselves to good use, and this books will tell you (or your boss) how. Even if you don't go fully agile, this book will offer lots of advice and ideas, on how to improve you work as a manager.