I just picked up the G-Max GM55 half helmet and am pretty impressed. There may be others slimmer than this but it was supposedly designed to be slimmer than most. I has a retractible inner visor as well which is cool if you forget your glasses. There is a youtube video about it by helmetharbor.com.

Without question, the greatest invention in the history of mankind is beer. Oh, I grant you that the wheel was also a fine invention, but the wheel does not go nearly as well with pizza. -Dave Barry-