SpeedTree - SpeedTree is a powerful toolkit used to create 3D vegetation for video games, films, and animations.
Treeit - Can create awesome 3d tree models and export to obj file format.
Plant Factory - PlantFactory is packed with amazing features that deliver unsurpassed realism and performance. An essential tool for any VFX pipeline, PlantFactory will have you creating stunning digital art in a flash!
The Grove 3D - Model or grow adaptive 3D Tree models for use in CG renderings.
Tree Studio - Easy 2D Tree Creation
Xfrog - Xfrog is a procedural organic 3D modeller that allows you to create and animate 3d trees, flowers...