I picked up a poly stretch tube from Nashbar years ago. It goes around my neck, stretches up the back of my head under my helmet when it gets a little colder, and comes up over my chin and mouth when it's colder than that. It generally takes me down to about 10*F. Then I start moving to a balaclava, usually a fleece scarf wrapped various ways, then finally at about -10*F I add a neoprene face mask. I've switched to full sealed goggles by then too, because at -10*F and lower you have to have NO exposed skin or you get frost nip.