If you plan to ride w/any regularity in the winter, winter cycling shoes/boots are an excellent investment.

I have Sidi Diablos and the Lake winter boots [was able to get both on sale but they are worth the money, even if you have to pay full price]. The latter are my Herman Munster boots--a bit clunky--but they are decently warm. The Sidis are warm, too, but I have outfitted them w/toe warmers and boot covers. My feet are WIMPY and get cold quick. Wool socks are a must. Denise is right that the midweight wool socks, paired w/chemical footwarmers, seems to work best in most conditions. I also like the Woolie Boolie socks. Since my winter shoes/boots are a size larger than my usual and allow for more air circulation, I will use thicker socks when it's brutal. If I use them on moderately cold days, I end up w/wet feet (my feet sweat a lot).

Hands are also difficult. I use wool glove liners with AmFib lobster-style gloves. On really cold days (below 35 or so), I use chemical hand warmers, too.

Wiggling your toes/fingers helps to keep the blood moving some, too.

Usually, the first few really cold rides are tough. My body tends to acclimate a bit. Even though my hands & feet will invaribly get cold, I'm able to deal with it better. I suppose it's a matter of getting tougher, mentally, to the discomfort.