All of the above are great ideas, particularly the point about blood circulation.........Last winter I wore SealSkinz socks made with a fleece liner. They made a big difference when worn over a wool sock in my roomy winter riding boot. (The winter boot is a size larger than my warm weather shoe, to allow for layering.)

If your shoe has enough space at the toes, you can add a Heat Grabber or other small chemical warming pack. (@$1 pair) Let them heat up for 5 minutes or so before you put them in your shoes. If you ride less than 3 hours, they'll be good for at least a second ride. Just take them out of your shoes and immediately wrap them tightly in foil to cut off the air supply so they'll cool down to 'dormancy.'.....The packs work well in gloves, too. Don't use them directly on your skin. Have at least a thin layer between you and the pack.

Have fun!! Winter riding is great when you're dressed for it!