I use a Garneau Globe; it's a great helmet at a really good price. I've used all manner of other helmets in the past--Giro, Bell, Specialized, Trek--and this one fits as well or better than any of the others. It's really well ventilated, too; I can really feel the breeze coming throught the vents.

As long as Garneau continues to make helmets, I'll be a loyal customer.