Succeeding with Agile: Software Development Using Scrum Mike Cohn is one of the top Scrum experts. This book is a must-read for all Scrum practitioners.
Agile Software Development with Scrum (Series in Agile Software Development) Schwaber and Beedle's book that started it all!
Exploring Scrum: The Fundamentals Practical real-world advice from two of the most experienced Scrum practitioners in the world.
The Agile Team Handbook Jan is one of the first to cover teams in Agile!
Head First Design Patterns: A Brain-Friendly Guide Quality code requires the use of Software Design Patterns. Start here!
Multi-Paradigm Design for C++ Don't let the C++ scare you away! James has great advice for good design.
Design Patterns Explained: A New Perspective on Object Oriented Design, 2nd Edition (Software Patterns) Tried to read the GOF Design Patterns? How did that work out for you? Shalloway translated by Jim Trott make it make sense!
Practices for Scaling Lean & Agile Development: Large, Multisite, and Offshore Product Development with Large-Scale Scrum Need to scale? Start here.
Lean Software Development: An Agile Toolkit Lean Software Development beginnings.
Implementing Lean Software Development: From Concept to Cash The real value of Lean in software development. Lower your Concept to Cash time.
Specification by Example: How Successful Teams Deliver the Right Software The bible on Acceptance Test Driven Development using Fitnesse.