Crucial Conversations: Tools for Talking When the Stakes are High by Kerry Patterson, Joseph Grenny, Ron McMillan, and Al Switzler.
As you can see from the list of books below, over the past year I've been a student of conversation and relationships. I've been especially interested in how we can make our conversations more rewarding for ourselves, for others, and for our relationships. Crucial Conversations helped me to make a big leap in that direction, and that's why it is my favorite book of 2003. [Full Review]

Other favorites:

Difficult Conversations: How to Discuss What Matters Most by Douglas Stone, Bruce Patton, and Sheila Heen.
Difficult Conversations shows that any conversation that matters is really three conversations: one about what happened, another about how we feel about what happened, and a third about how all of that affects the way we think of ourselves. When we try to talk about all of these important things at once, each conversation confuses the other, and we derail the overall conversation.
The second half of the book describes how to conduct a learning conversation, a conversation in which we learn the other person's story, express our views and feelings fully, and solve problems together. These ideas are very similar to the concepts in Crucial Conversations of dialogue and the "shared pool of meaning," and also to the approach I describe in my articles "Resistance as a Resource" and "Untangling Communication."
Difficult Conversations and Crucial Conversations complement each other nicely. The books cover similar content, and express compatible ideas about how to make challenging conversations work.
Don't Be Nice, Be Real: Balancing Passion for Self with Compassion for Others by Kelly Bryson.
How to move beyond understanding each other to empathizing with each other. Expands on Marshall Rosenberg's Nonviolent Communication (below). [Full Review]
The Flawless Consulting Fieldbook & Companion: A Guide to Understanding Your Expertise by Peter Block.
Peter Block and colleagues describe lessons they've learned from their experience of practicing the principles of Block's Flawless Consulting .
Leadership and the New Science: Discovering Order in a Chaotic World, Revised edition by Margaret J. Wheatley.
Wheatley applies principles from the "new sciences" of chaos, complexity, and self-organizing systems to leadership and human organizations.
Longitude: The True Story of a Lone Genius Who Solved the Greatest Scientific Problem of His Time by Dava Sobel.
The story of how clock maker John Harrison solved the problem of longitude. The difficulty Harrison experienced in gaining acceptance for his solution, despite the gravity of the problem, makes this a fascinating case study of resistance.
The Illustrated Longitude , by Dava Sobel and William J. H. Andrews, has the same text as Sobel's original book, with the addition of 180 marvelous photographs and illustrations, each described in detail.
Loving What Is: Four Questions that Can Change Your Life by Byron Katie.
Katie describes "The Work," a set of good questions by which we can identify and inquire into beliefs that cause stress and interfere with our communications, relationships, and happiness. Includes transcripts of many sessions in which Katie facilitates many people to inquire into their beliefs to resolve a wide variety of painful situations.
A CD version of Loving What Is includes live recordings of people doing "The Work."
Narrative Therapy: The Social Construction of Preferred Realities by Jill Freedman and Gene Combs.
Narrative therapy invites people to make visible the stories that create and sustain the problems with which they are struggling, and to create alternative stories that better support meaningful and fulfilling lives.
It was from this book that I began to understand the importance of stories and the influence that stories wield in our interactions and relationships. Also enlightening for me was the chapter about helpful questions.
Nonviolent Communication: A Language of Life, 2nd Edition by Marshall B. Rosenberg.
How to move from moralistic judgments — judgments that imply wrongness or badness on the part of people who don't act in harmony with our values — to clearer, more effective ways to express our needs.
Rosenberg's Speaking Peace is an audio version of these ideas.
Open Space Technology: A User's Guide, Second Edition by Harrison Owen.
Open Space Technology, a simple and powerful way to organize meetings and conferences, encourages passion, commitment, and personal responsibility, and taps the capacity of a group of passionate, committed, responsible people to self-organize to address complex issues.
See my earlier article about Open Space Technology and Owen's book.
Turning to One Another: Simple Conversations to Restore Hope to the Future by Margaret J. Wheatley.
Wheatley encourages us to hold conversations about what matters most to us. Nothing fancy; just simple conversation. Simple and powerful. [Full Review]