Just came upon this site and found it interesting. Thought others might as well. Has some of the more popular motorcycle helmet tests.
http://www.nhtsa.dot.gov/cars/testing/comply/fmvss218/
It appears that at least in the 2006 test report that if you click on the "HS #" for the specific helmet your interested in, it will bring up another very extensive testing page with data analysis on that helmet.