HEAD

dot_clear.gif (42 bytes)Regardless of a flourishing crop of hair, the scalp is a wonderful radiator. Wouldn't want the brain to overheat! The first chore when it gets cool is to reduce the breeze up there.
You can find a little polypropylene skullcap in the catalogues. It can cover your cold ears as well. And a helmet cover is next.
When it gets really cold a balaclava is in order. You can find them in silk, polypropylene or wool. Here again, layering works (as long as both layers are really thin and fit OK under your helmet.) And you might think about carrying a dry balaclava to change if you're sweaty after any lull in the ride.

When it's nearing single digits you will want to use Vaseline on any skin you can't cover - and maybe make that a minimum with ventilated goggles. 

Do check out IceBike, the best Winter cycling source on the web, for much more information.