If it snows, drive or bus. Icy days are the same. Cars can't stop hitting each other nevermind cyclists. Dry and cold is fine if you can stay warm. Rain is fine as well. Traction is a not as good, but just be a bit more careful and you'll be fine.
With the shorter days, invest in a good rear blinking light. Spend a bit more to get one that is brighter. For a front light, there are some pretty decent and cheap front lights that are fairly bright. They are not bright enough for trail riding, but they let cars see you which is what they are made for. If you are buying new tights and jackets get ones with reflective stripes. You can also buy reflective ankle bands or other similar things for $3-8.
Staying dry. Fenders are the key. What soaks you on a ride in the rain isn't the water falling from the sky, it is the water spraying off your tires. Getting decent fenders that fit on front suspension might be an issue. I prefer full coverage fenders (big kinda dorky ones), but the clip-on ones work ok. This will keep you from being completely soaked.
http://www.rei.com/bike/TOC/Components/Bike+Fenders?cm_re=toctocbike_fenders[HTML_REMOVED]vcat=REI_SSHP_CYCLING_TOC
Your feet will still get wet so you can use plastic shopping bags inside your shoes or spend more for waterproof booties that fit over your shoes. Again get ones with reflective taping.
http://www.rei.com/bike/TOC/Clothing/Cycling+Shoe+Covers?cm_re=toctoccycle_shoe_covers[HTML_REMOVED]vcat=REI_SSHP_CYCLING_TOC
A decent gore-tex rain jacket will be nice, but if you have fenders is not totally necessary (I haven't used a gore-tex jacket, well ever). Long sleeve synthetic jerseys under a good windbreaker jacket is pretty much what I use. As it gets colder I add more layers and/or use heavier jackets. I have some thin fleece gloves that are big enough to fit over my regular cycling gloves. They keep my fingers mostly warm until about -5C (~25F). A bandana or headband keeps my ears warm. Another bandana keeps my neck warm. I use my rain booties to keep my feet warm (with heavier socks of course).
Keep on commuting! I always feel better when I've ridden to work even when the weather is a bit ugly (which in Vancouver is pretty much the next 5 months). Dress warm, and make sure that you can be seen. Oh yeah, stash an extra set of batteries in your pack next to your spare tube just in case the ones in the lights die.
Dave