I found a great new tool today. It’s called Dryad, a tree generator that is free for any use. Currently, Dryad is available for Mac and Windows. You will need a good Internet connection, because Dryad downloads user generated trees off the Dryad site, and also uploads information about the trees that you chose.
When you find a tree you like, just click the check mark button, and Dryad makes a Wavefront .obj file, which can be imported to Blender. Sweet!