Here's a small sample of some treehouses or makers that capture my imagination, partly be because I'd like my own home to be a bit like a tree house (but also a beach house, space pod, 17th century castle etc.)
In the UK - Blue Forest Treehouses build bespoke or commercial for adults and for kids. They have also just started to build Eco-Lodges, the first one being in Spain.
The Treehouse Company built my favourite UK treehouse at Alnwick Castle. It's frightening to think what the Alnwick treehouse cost to build when you realise that the Magical Treehouse in Fife, Scotland (2nd photo below) cost over £40,000! (their website won't work in Firefox, use Explorer)...
Not for the feint hearted, this has an incredible spiral stairway taking you up to the Cedar Creek Treehouse Observatory in Virginia.
Free Spirit Spheres are completely circular units that can be hung in the trees or anchored to the ground.
o2Sustainability have made a geodesic looking dome type of eco-treehouse which looks incredible lit up at night so for me it fits with my treehouse love AND my love of lighting.