I've got two bikes for winter duty, depending on conditions.
My old Sirrus road bike, for when it's dry and clear, since I'm more partial to raod riding. Just equipped it with fenders, and a Specialized armadillo tire for the rear, and one planned for the front once that wears out. Fixing flats in the cold is not fun. MTB pedals and shoes for better traction.
And for when it might be snowing a bit, or the roads are sloppy, my old Stumpjumper. Sometimes with MTB pedals, sometimes with flats. haven't gone to studded tires yet, but I do plan to get a pair someday. Personally, I like this more for winter riding, as it's slower(nice when it's cold), it's a bit more stable and slower handling, and the upright riding position offers better vision and center of gravity. Plus, it's got braze-ons for rack and fender mounts. You can pick up a late-80's/early 90's steel framed mountain bike with front and rear braze-ons on ebay for $250 or less.
