If you want your feet to stay dry in adverse conditions then Sealskinz are your natural choice.
Sealskinz are particularly suited to activities where your footwear in not waterproof and you need to keep dry. A perfect example of this is mountain biking in winter. Until you try biking with Sealskinz socks you will never know how much better life can be!
Even though Sealskinz are waterproof they remain breathable. You may imagine that they are like wearing plastic bags over your socks but they are nothing like that.