I too applaud the buff, I wear it from about 40F all way up to "why the hell am I biking in weather this hot?"

Below 40F I switch to one of my favorite pieces of gear, a super-super-light-and thin polartec fleece beanie. It's Mountain Hardwear and I bought it for less than $5 at REI many years ago. It's so light I could probably conceal it completely in my fist and it's just long enough to cover the top halves of my ears. I also like that you can rinse it out with warm water at work or home, wring it out, and it'll be bone dry in just a couple hours. I wear it alone under my helmet from about 30-40F and over a thin polypro or thin smartwool balaclava below 30F calm or below 35F windy. I find the balaclava/super thin fleece beanie combo works great all the way down to about single digits and then I swap the beanie for a very snug fitting REI softshell beanie with ear flaps over the same balaclava.

Today it was a windy 1F when I left home in Boston for my 10 mile commute. Since my two balaclavas (polypro and wool) are very thin, I wore both of them with the softshell beanie and subbed ski goggles for my normal cycling glasses. Except for the top of my helmet forcing the goggles down on to my nose a little too much, it was great. I might search for some just slightly lower profile goggles and I think I'll be all set for anything. Also, I never tape or cover my helmet vents and have no regrets.