Virgillia Capensis (syn: virgillia oroboides) is a tree that I don't hear about much in permaculture discussions. Its fast growing, frost resistant and wind tolerant. It seems ideal for my windbreak so I bought some; and now that I've got them I notice they are used a bit by the local council here in Tasmania (south of mainland australia).
What I don't know is if they are nitrogen fixing. They are in the Fabaceae family so I think there is a fair chance they are. I'd love to hear from people who have experience with this tree.