I ran across this book a couple of weeks ago and ordered it immediately. My dream to live in a treehouse is second only to my dream to live in a kelp forest (and the treehouse seems a bit more feasible).
Taschen published this gorgeous book by Philip Jodidio featuring 50 treehouses around the world. From tea treehouses to hotel treehouses to virtual renderings of speculative treehouses, each has a detailed description, beautiful photos, and an incredible illustration by Patrick Hruby. And (as if I needed another reason to love this book) the index is a map.