My most often used winter-commuter is the Marin Nail Trail:

Single-speed, disc brakes, depending on the conditions, either studded tires or Top Contact (non-studded winter tires). This bike is bomb-proof for harsh winter conditions. (excited for next months upgrades including new Surly Troll fork and full coverage fenders).

I have used the Kona Dew Drop:

Nothing wrong with this set-up, except I have no winter tires for it ...and pay the price from time-to-time (read as falling down). I've been thinking about a set of 700 studded tires for it to give me more options than just the Marin.

My ULTIMATE winter commuter would be a Pugsey with studded Dillinger tires. Some float for the fresh snow, some studs for the ice, and generally bad a $$ bike. Sadly, the CFO has not freed up the capital for bike #6 in my collection. In Minneapolis area, we have our first winter storm today, forecast for up to 12 inches of snow (looking unlikely now)... with that amount of snow, I leave the bikes at home, none of my bikes are worth a damn in that much snow.