Here is a rather long reading list that I have assembled over the last few years. Books marked with an asterisk (*) are those I have read and personally recommend. The rest are those I have found to be frequently recommended by other Agile practitioners. Within each section the books are listed more-or-less in the order that I value them.
Agile methods and principles
*Agile Software Development with Scrum by Ken Schwaber and Mike Beedle [the “Black Book”—essential reading for good ScrumMasters]
*Agile Project Management with SCRUM by Ken Schwaber [the “Gray Book”—supplements the first Scrum book with real life examples]
*The Enterprise and Scrum by Ken Schwaber [essential reading for coaches and for enterprise rollouts]
*Extreme Programming Explained by Kent Beck [a great book for team members]
*Lean Software Development by Mary Poppendieck and Tom Poppendieck [A good intro to Lean]
*Implementing Lean Software Development: From Concept to Cash by Mary Poppendieck and Tom Poppendieck [a great read for managers who want to understand Agile]
*Agile Software Development – The Cooperative Game (2nd Edition) by Alistair
Cockburn [a very inciteful view of product development]
*Organizational Patterns of Agile Software Development by James O. Coplien and Neil B. Harrison [a great book for software architects and other team members]
Agile Software Development, Principles, Patterns, and Practices by Robert C. Martin
Agile Software Development in the Large: Diving Into the Deep by Jutta Eckstein
The Art of Agile Development by James Shore
Additional context
*The Mythical Man-Month: Essays on Software Engineering by Frederick P. Brooks [a classic]
*Peopleware: Productive Projects and Teams by Tom DeMarco [another classic]
Slack by Tom De Marco
Joel on Software: And on Diverse and Occasionally Related Matters That Will Prove of Interest to Software Developers, Designers, and Managers, and to Those Who, Whether by Good Fortune or Ill Luck, Work with Them in Some Capacity by Joel Spolsky
Debugging the Development Process: Practical Strategies for Staying Focused, Hitting Ship Dates, and Building Solid Teams by Steve Maguire
Teamwork
*Facilitator’s Guide to Participatory Decision-Making by Sam Kaner (2007) [a gold mine for coaches]
*The Wisdom of Teams by Jon R Katzenbach and Douglas K Smith (1993) [a bit dated, but still useful]
Collaboration Explained by Jean Tabaka
The Five Dysfunctions of a Team: A Leadership Fable by Patrick M. Lencioni
Continuous improvement
*Agile Retrospectives: Making Good Teams Great by Esther Derby and Diana Larsen
[essential for ScrumMasters and coaches wanting to run good retrospectives]
Project Retrospectives: A Handbook for Team Reviews by Norman L. Kerth [the classic text]
Accelerating Process Improvement Using Agile Techniques by Deb Jacobs
Requirements and planning
*User Stories Applied by Mike Cohn [essential reading for good Product Owners]
*Agile Estimating and Planning by Mike Cohn [essential reading for good Product Owners]
Development practices
Refactoring by Martin Fowler
*Test Driven Development: By Example by Kent Beck.
Pair Programming Illuminated by Laurie Williams
Refactoring to Patterns by Joshua Kerievsky
Test Driven: Practical TDD and Acceptance TDD for Java Developers by Lasse Koskela
Practices of an Agile Developer: Working in the Real World by Venkat Subramaniam
Release It!: Design and Deploy Production-Ready Software by Michael Nygard
The Pragmatic Programmer: From Journeyman to Master by Andrew Hunt and David Thomas
Working Effectively with Legacy Code by Michael Feathers
xUnit Test Patterns: Refactoring Test Code by Gerard Meszaros
Continuous Integration: Improving Software Quality and Reducing Risk by Paul Duvall, Steve Matyas, and Andrew Glover
Refactoring Databases: Evolutionary Database Design by Scott W. Ambler and Pramodkumar J. Sadalage
Code Complete: A Practical Handbook of Software Construction by Steve McConnell
Domain-Driven Design: Tackling Complexity in the Heart of Software by Eric Evans
Pragmatic Project Automation: How to Build, Deploy, and Monitor Java Apps by Mike Clark
Agile Project Management
*Agile and Iterative Development: A Manager’s Guide by Craig Larman
[provides a useful overview and comparison of the main Agile development methods for those who don’t know which method to choose]
Agile Project Management: Creating Innovative Products by Jim Highsmith [this book is on the list because so many other people recommend it; I have read it and I don’t]
Manage It!: Your Guide to Modern, Pragmatic Project Management by Johanna
Rothman
Managing Agile Projects by Kevin, J. Aguanno