1. Head First Design Patterns
The book is fantastic - I've done a bit of work with design patterns in the past but this book really helped to put them in context, and the way the information is presented is very conversational, fluid and light while at the same time driving the concepts home. It's very much a "both sides of the brain" book, unlike some of the more onerous tomes that try to explain patterns in a generic text-only manner.
It's so good that I've just purchased a bunch of copied for the team.
2. Agile Project Management with Scrum
I posted earlier about some of the problems I encountered implementing Scrum. This book really helped me reassess what I was doing wrong and showed how I could improve what I was doing.
At first I was a little thrown out since there isn't a great deal of instructional "do this" information. Instead the book consists of a range of different scenarios, what the issues were in the scenario and how scrum was applied to produce a positive result.
It also covers some of the mistakes and errors that can be made while implementing scrum. If only I had found this book earlier!
If you plan on implementing scrum, grab this book and read it first. It will help get your mind into the right way of thinking, and give you tips on how to communicate your changes to the rest of the business.