here are several
http://www.veganhealth.org/articles/dxrates
Also, what about the studies showing the children of vegan (it might even be vegetarian, can't recall) mothers have lower birth weights, IQs, and are shorter than the general population? What about the rates of B-Vitamin anemia?
I think that the benefits of being a vegan are the benefits of being concerned with your health. I'd be interested to see a comparison between an equally fastidious group of meat eaters.