I think this one, along with a modified shader specifically for trees, will be a big winner. It's the only program I've used that is pretty close to doing it by hand.
The program is called tree[d]. I tried it out awhile ago, and walked away annoyed, because it was nice but it only exported B3D and X formats, both of which are distinctly non-portable unless you can afford Polytrans or like being frustrated with the free tools.
The coder apparently came back to it, and the current version allows for OBJ export, can be used to build branches for billboards that you can then use in the program very easily, has good low-poly functions using simple billboards (if there's interest, I can prolly explain how to do it, as that's not entirely easy) and is, in short, a very very nice tool to make good trees with at different polycounts, and it has built in tools for rendering LODs for billboards.
This is for a high-poly environment, 965 tris:
RTS spec, 163 tris:
