It's all about the boots, baby!
I layer my feet- I have real bad problems with keeping my hands and feet warm, even when it's in the 60s and 70s. For temperatures like what you describe, I definitely layer- first I put on the thin layer of polypropylene socks. Then I put on a pair of coolmax socks over that. I have a nice pair of mountain bike shoes that work well for me. But it makes all the difference in the world when I add my neoprene boots over the shoes. If it's seriously cold (towards the -15 to -20 C range), I'll also put on a pair of nashbar hytrel socks over the coolmax socks, then put on the mountainbike shoes, then the neoprene boots.
My feet never get cold anymore. Yay!
I got lucky- the Perfomance store in my area had a huge sale on their neoprene and polypropylene products, so I got the neoprene boots at half off! I paid $20 for shoes that normally go for $40 or so. My plan is to buy all my winter gear for NEXT winter sometime in April so I can get all the stuff I really would like to get but couldn't afford when it's seriously on sale.... I am definitely going to ride all winter next winter, and I want to be as prepared as possible. This is my first winter riding outside all winter.
Get the boots!
Koffee