You might also want to look at Gath helmets.
http://www.gathsports.com/ My principal concern right now is ear protection. I bought the Gath convertible surf model and it seems to be pretty good; it's comfortable, light and I can hear pretty well with it on. I haven't tested it out with any serious falls yet. From the pictures, however, the original Gath surf hat looks like it would provide better ear protection