Forever Young Treehouses http://www.treehousefoundation.org/
Forever Young Treehouses is a private non-profit organization that inspires, helps, designs and constructs universally accessible treehouses for schools, camps and the communities that serve people of all ages and abilities.
Living Tree, LLC. http://www.livingtreeonline.com/
Commerical treehouse builder. An ISA Certified Arborist with 41 years experience building treehouses. Picture gallery.
Treehouse Bed and Breakfasts http://bandb.about.com/cs/uniquegetaways/a/treehouses.htm
Accommodations available in locations around the globe, from Alaska to Hawaii, from Turkey to Papua New Guinea.
Cedar Creek Treehouse at Mt.Rainier http://www.cedarcreektreehouse.com/
Nahiku -- Maui http://www.nahiku.com/
Lothlorien Woods Hide-A-Way -- Portland, OR http://lothlorienwoods.com/
Suwannee River Lodging -- Florida http://musicliveshere.com/luxuryCabinRentals.asp
Kadir's Tree Houses -- Turkey http://www.olympostreehouses.com/