You should certainly get a helmet that is DOT certified. But, the Snell rated helmets, due to their need to withstand a very high amount of force, are actually TOO stiff. My uncle was an ER surgeon and avid motorcyclists and always kind of theorized this, but I never really gave it too much thought until I started looking at helmets for my bike, and I stumbled across this article:
Motorcycle Helmet Design, Helmet Standards and Head Protection - Gear Box - Motorcyclist Online
Very interesting, I think. Any thoughts?