Depends on the windchill, but down to around freezing I make do with a neoprene cap under my helmet that also covers the tops of my ears, and a zipped up collar. The collar then gets unzipped about 5-10mins into riding...

With high winds +/or lower temps though I would consider a full neoprene balaclava, a Buff around my neck and possibly ski goggles. Wind in my eyes is worse than wind in my face, it dries my eyes out horribly.

What's funny is that a year ago in this weather I would've ridden with a fleece lined jacket over a few t-shirt type layers, and a full scarf, cotton hat under the helmet and feel all sorts of wrong. Thank you BF for educating me.