don't know of anything to generate tree native in blender, but for tree gens that can then be imported there are Dryad, Arbaro and POVtree. Dryad is pretty cool but I've had issues with opengl on some machines (like my laptop - the intel graphics don't do gl very well :( ).

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Toolset: Blender, GIMP, Indigo Render, LuxRender, TopMod, Knotplot, Ivy Gen, Plant Studio.