SpeedTree - SpeedTree is a powerful toolkit used to create 3D vegetation for video games, films, and animations.
Blender - Blender is the open source, cross platform suite of tools for 3D creation.
Tree Studio - Easy 2D Tree Creation
Cinema 4D - Cinema 4D is a 3D modeling, animation, motion graphics and rendering application.
ngPlant - ngPlant is a plant modeling software package.
Autodesk Maya - Maya is 3D computer animation software with powerful modeling, rendering, simulation, texturing, and animation tools for artists, modelers, and animators.