+1 on the Bern helmets. I have a Bern Watts Hard Hat that I use as a bike helmet and a snowboard helmet. It has a visor and a furry snap-out ear flap that goes all the way around the back of my head and a good ways down my neck. They do run small though, so either try one on or order 2 sizes too big. The Watts is also great because it has vents in the top that allow me to use it in the warmer months without the flap. The do offer one without the vents though if that's your thing.

They're kind of pricey but you can get them on clearance from REI or through the interwebs for much cheaper than normal retail.

Thanks everyone for the advice. I'm thinking I am going to give a vented one a GO and see where we're at. I'll let you know my findings.

I've used my snowboard helmet in -20C and below. I like it. Goggle friendly - warm ears etc. YMMV.
I have a wool skull cap (under hardhat) from the construction or logging industries, which is the warmest skull cap I've tried. The snowboard helm works better than the wool skull cap and a bike helm, but when I put the skull cap in the snowboard helm I could withstand Antarctica I think :-)