I also like "101 Games for Trainers" by Bob Pike, and "Games That Teach Teams" by Steve Sugar. I think these three books together are the best place to start -- there are a lot of other titles out there that are, in a word, garbage, and should be avoided.
As a communications trainer with my own non-profit board to deal with, I was most impressed by the fact that the chapter on non-profits identifies as a "most common concern" exactly the thing that causes my board trouble -- complaints of micromanaging on details while sidestepping needs for fundraising. The insight that this is a structural problem rather than a personality issue has been extremely helpful to me -- even without a retreat -- and convinced me these authors must know what they're talking about.
I am in a related, but quite different, field. As a qualitative research moderator, I am often asked to facilitate meetings or retreats by clients who are unaware of the differences -- hence, my interest in this book. But, whether you are working for a small or large company and want to hold a retreat, or you are someone needing to actually facilitate such an event, this book is a wealth of information. And for anyone thinking of facilitating a retreat or just understanding what a facilitator must be able to do, they would be advised to read the "definition" or role of the facilitator on page 116!
I found this book very well-written, easy to read and follow. It's filled with lots of practical information and tips, valuable time estimates for the various activities, and additional resources given.
The creative thinking section was particularly interesting to me. As a "left brain" person, I am usually skeptical of these kinds of activities. But the authors' examples and explanations of each exercise gave me a new appreciation for the value of this type of retreat.
I also visited the authors' or book web site, which is a nice accompaniment to the book, including additional resources.