Up here in the PNW we tend to get a lot of rain, but not as much bitter cold so most of my suggestions are about keeping dry....

My feet tend to sweat, even when its cold out, so I've never been a fan of the plastic bag thing - I end up just as wet.... On the other hand, I love my winter Sidi shoes with a nice cushy pair of wool socks. Nothing will ever keep your feet perfectly dry, but the dedicated winter shoes come close. A couple things you do have to do - make sure your socks do not poke out over the top of the neoprene cuff - the water will travel right down your sock and into the shoe. Pull your tights well over the shoe - down as far as they will come - also directs water away from the cuff of the shoe. That setup will be virtually water proof for a few hours at least and windproof all of the time. The best thing - no holes that go all the way through the bottom, so no fountains of cold water hitting the soles of your feet - heavenly. On plain cold days you feet will never even know its not nice out.

One thing you will want if you will be riding in the rain at all is fenders. Full coverage if you can fit them, but even speed fenders can make a big difference. Be sure to extend them to protect yourself and anyone who might be riding behind you. A nice big flap on the front one will keep a lot of water and muck away from your feet in the first place! A nice big flap on the rear will keep same said muck out of the face of anyone who might ride behind you.

Another good investment is tough tires - choose your brand (conti gator skins, specialized armadillos etc), but get a pair that are made for adverse conditions and won't flat easily. You'll appreciate not standing around in the rain trying to change a flat with numb fingers.