Mountain Hardwear Windstopper Micro Dome

This hat is simply wonderful. I've used it in during the cold Aomori winter, and never felt warmer or more comfortable. I used it running at right around freezing and it breathed great, wicked the sweat away, and kept my head perfectly cozy, but not too warm.

The one negative thing, though I'm not really sure that its really a negative, is that sound doesn't penetrate the material very well. You can still hear, but not as well as with other beanies.