I have a Protec snowboarding helmet that I use during the winter. I know tat it's not biking specific, but it does well. The BMX Protec that I have of theirs has too many vents. The snowboard one has ear flaps, and the padding on the inside is held on with velcro, so you can use different thicknesses depending on the thickness of the hat you're wearing under it. I've used it down to 30 below.
Thankfully I haven't had any real impactswith it, but I figure if it helps someone who hits a tree at 30mph, it will help me. I go slower in the winter anyways.