This is amazing if you have an iPad. Free, too. You can basically grow 3D tree models by drawing on the screen, and not just trees, I've even made some vines and bushes and weird alien lattice things in my short time playing with it. They're exportable, too. I haven't checked anything like poly count yet, though.
You can't add your own textures within the program yet so far as I can tell, but it's still pretty darn cool. And the documentation is great.