In reply to chrisbussell:
Cheap solution - decathlon overshoes, about £12
Fairly cheap - seal skins , about £30
Expensive - northwave boots - about £100
Have to say I've not been that impressed with the boots, bit too stiff for my liking, particularly for winter mountain biking, but may be alright for commuting .
Likewise the overshoes don't work too well if you have to walk through snow, but do keep the rain out.
The socks keep your feet dry, but your shoes get wet.which may be a problem next day