I made a major step forward in staying warm today by purchasing some cycling booties. That’s what I call them, I guess some people refer to them as shoe covers. Not only do cycling booties keep your feet warm on a frigid day, some models are also waterproof. Just wear your waterproof pants over the tops of the shoe covers and you’re one solid piece of waterproof protection. Like most things, there are cheap inexpensive models, and more expensive ones. The good thing about bicycling shoe covers is good waterproof models are available for a low price. For 50 dollars or less you can secure a nice pair of waterproof shoe covers.
Check out the Sugoi Resistor Bike Booties at REI.
If the weather is cold but not cold enough to wear full shoe covers, you can also buy toe covers. These slip over the toes and cover up the ventilation areas on the toe. They cost less than 20 dollars usually.
Check out these Pearl Izumi toe covers
Bicycle Touring for the Long Haul 