I am not prone to getting cold very often, but when I do it is almost invariably my feet that suffer. And there is nothing more uncomfortable than cold feet, or the inordinately long time it takes to warm them up again.
After having mentioned this repeatedly to my fiancee I was recently given a pair of Western Mountaineering Down Booties as a gift. They are, I will be the first to admit, absolutely ridiculous looking when worn, but also the warmest things I have ever had the pleasure of wearing on my feet. Designed for winter camping, they are filled with 800-fill power goose down that provide an impressive amount of insulation (which, when puffed up around your feet, also gives the impression of wearing clown/astronaut shoes).
Unlike other models designed solely for wear around the house, the WM down booties have a tough and water proof bottom (with a thin layer of foam insulation) that can be worn while camping or on quick trips to the mailbox. Another useful feature is an elastic collar that wraps around the ankle that traps in hot air (similar to a down collar in a sleeping bag). This amount of warmth the down provides is impressive and far greater than any other slipper I’ve tried. The fact that they weigh 6-oz total (while being significantly compressible) means I can easily travel/camp with them.
While the booties are not cheap they are definitely worth the cost to keep my feet warm around the house (while also allowing me to turn down the thermostat a degree or two) or while out camping on a cold night.
[Note: For those looking for something more appropriate for wear in a sleeping bag I have heard great things about the domestically produced Goosefeet Down Socks. --OH]