When it comes to protecting your feet, there are endless variations on the market. We prefer an overshoe, which typically has a zippered opening in the rear to make pulling them on and off easy. Make sure you check the sole coverage before investing, though--the more you cover, the warmer you'll be.
Neoprene overshoes have the added advantage of protecting your feet from water and keeping them from freezing if dampness does slip in. On the flip side, booties are a more sock-like option--they'll keep your feet warm, but most aren't waterproof.
Lastly, toe covers are a quick, easy option for early spring or winter, when the temperatures have dropped enough to cause discomfort but not enough to warrant full coverage. Quickly slip them onto the toe box of your shoe to provide instant warmth.