Here's another vote for the Ice Kings. I've had a pair for probably 10 years and I love them. My feet have yet to get cold, and I've bowhunted in single digit temps in a pair of standard white cotton socks (back in my younger, and stupider days).

Another thing I've found that's great and that I've been using a lot is ThermalFeet. Basically they're a booty that slips over the outside of your boot and has a pocket to hold a Hot Hands type handwarmer on the top of your foot to keep the blood circulating into your foot warm. The best part is that they're small enough to slip into your pack, until the Arctic Shield boot covers, and thus far have kept my feet nice and warm. Check them out at www.thermalline.com I just got a set of the updated ones for 2007 and they're awesome. Same principle as the ones on their website, but instead of a bungee cord to hold them on, they are more of a hospital type booty that slips over your entire sole and around your heel to hold it on. Good stuff!