I tried various full fingered cycling gloves and found that my hands were still getting cold on those really cold commutes so I finally started wearing a pair of snoboard mittens (thin ones) over the top of standard full fingered cycling gloves. Ahh, warm hands!
I also invested in a pair of Lake Winter Cycling boots which will keep your feet warm and dry on those rainy days. Expensive but if you are serious about winter commuting, worth the money IMHO.
You are also going to need fenders for you bike (I use Planet Bike Cascadia), reflective gear for your body and a good set of lights, front and back (I use Dinotte).