I like my smart wool balaclava. It's warm for me (with a hat) down to like 10 below (it doesn't really get colder than that here). I should point out, I have a beard and that may make it seem warmer to me.

I pair it with ski goggles on the cold days. The two can cover every bit of skin on my face, head, and neck. It's light weight, simple, and warm even when it's soaked. It keeps my breath pretty warm and moves out of the way when I don't want to cover my mouth.