Forester is a cheap solution to quickly generate trees or plants for use in game design. It is configured to export its content right into a game engine, without having to modify it, that is why I list it here. I think it is the only tree generator that currently supports Torque3D. The price is $30, but they also offer template packs for $10 each. It may be a bit complicated to generate your own trees, but if you want to buy the templates you can have some trees ready within minutes.