Freshome blog has a neat article about the 8 most amazing tree houses in the world.
I really like this one by Takashi Kobayashi, Japan's leading treehouse creators (how many treehouse creators are there in the whole world, let alone Japan?):
This house was designed after an advertising agency in Tokyo, hired him to design a treehouse for a Nescafé commercial now running on Japanese television. Mr. Kobayashi built an oval bird’s nest of a house, 12 feet high and 9 feet in diameter, reached by a circular staircase, and the final price for this tree house was about $38,000. The house is located on a field there owned by the town of Kamishihoro, where it remains an enticing, if off-limits, gift from Nestlé, the makers of Nescafé, to the people of Hokkaido.
Link - Thanks Neatorama Reader!