I just picked up one of those new fancy 6D Helmets at our local friendly dealer (PA Power).
I haven't gone for a ride yet, but it feels great trying it on and with the goggles.
Certainly not cheap, but the whole idea is better protection from smaller scale hits- plus good rotational protection. Of course still excellent 'hard hit' protection.
Hitting a tree limb or something at 15mph could cause serious issues with a standard helmet. Reports are that this one is MUCH better for that sort of thing.
A buddy just got hurt pretty badly on a road race track and it really has gotten me to thinking about having maximum protection. Large and smaller impacts.
Go check them out!
Mark