After the bike your gear is going to be crucial to making your commute as comfortable as possible... there will be a debate on whether or not to run studded tires and since I use both on several winter bikes can say that you can get by really with non-studded tires as long as they are the right type. The rubber compound is even more important than the type of tread as a tire that gets hard in cold temps will not offer the same traction as a tire that stays sticky.

I have been running Schwalbe Hurricanes (semi slick) on my fixed mtb and Schwalbe CX Compe tyres on my cross bike and the hook up and control has been amazing despite the lack of studs. For ice the only real way to go is to use studded tires and I have a bike set up with these for when it gets really nasty and the iciest conditions here are usually in the spring when things start that thaw-freeze cycle.

Out in Alberta where we get a lot of cold and a lot of snow and slush staying dry and clean is really important so besides fenders, a waterproof and wind resistant shell as well as a waterproof footwear is essential. I am a huge fan of the polypro base socks at MEC as when they are slipped on under some woolies my feet stay really toasty.

Cotton is the work of Satan.

Your lighting should be such that people think you're a little screwy... you really cannot be too well lit up especially when winter commuting in Canada is a dark affair.

Plan on doing a lot of regular servicing as winter riding is hell on chains and drive trains and a dirty drive train robs you of efficiency at a time when your efficiency will already be compromised due to colder temperatures, bad roads, and gear that makes you less aerodynamic.