K2 Route helmet

Weighing in at 0.7 pounds, this helmet is the lightest on the market. It's also certified for both snow and cycling, so you could use it for both activities. And you just might: It features a unique Boa system that makes sure it fits snugly on even the most lopsided of heads, is equipped with removable earflaps, and boasts ample venting that should allow it to breathe, no matter how much you're sweating. [$150; k2skis.com]