I woke up today to find that it was around 10 degrees air temp with a windchill that put it around 2, factor in your speed moving on the bike and it starts to get pretty cold. A few weeks back I posted what I wear when it is 40 degrees, and here's the rundown for 10.
The outfit: full length Dickies, with thermal tights underneath. I prefer long johns to the lycra kind because my legs always feel like shit when I have tight ass clothes clinging to them. I like the freedom of movement traditional thermals provide. Wind shell with two long sleeve wool jerseys underneath. On the way home from work, it's usually a little warmer and if it's above 10 I'll usually just wear one long sleeve. The shell is a Patagonia Krushell that is no longer in manufacture. Coming from a climbing background I like outdoor companies products for outerwear rather than cycling companies. However many jackets in their line are cut for a harness and thus are fairly short in front and lead to the dreaded "red belly" from the cold and wind. This guy is nice and long, and the side and chest pockets double as vents. It's not very water repellent, but unless it's precipitating actively I prefer the breathability and will sacrifice waterproofness.
Glasses are a must, as is something around the neck. A large part of staying comfortable while biking is regulating your neck temperature effectively. I can unzip my jacket to vent the core while still having full frontal coverage.
Super awesome Chuey hat discussed in below post
Down Grandoe gloves: only good for 5 degrees and colder (remember the wind chill) otherwise too hot.
Awesome pink leg band, and neoprene shoe cover.
Winter cycling shoe. I hate these things because they pedal so much crappier than my regular shoes, but sometimes you need them.
So that's how I dress when it starts getting f'ing cold. If you've got winter wear tips, let's hear em.
stay warm and keep riding