If its warm to slightly chilly (greater than 45 degrees F) I just ride and enjoy not being hot and sweaty for once.
If it is chilly (30-45 F) I wear a base layer and a couple of long sleeve synthetic layers; for my legs I wear tights; in addition I will put on a pair of water resistant gloves or wool gloves, then I plastic bag my feet before putting on my shoes, and a rain cover for my helmet.
If it is nasty (less than 30 F) I wear a base layer, a long sleeve synthetic layer, and one or two wool sweaters; for my legs I wear tights (and for uber cold I will throw on a set of long underwear over the tights), a pair of water resistant or two wool gloves, plastic bag and double wool sock my feet before putting on my shoes, I usually wear some sort of balaclava together with a rain cover for my helmet.
As you can see, there is absolutely no rain gear in my list. I learned ages ago in the boy scouts that you are much better off expending your effort at staying warm than you are at keeping dry. Just keep the important stuff: feet, hands, and head dry in cold weather. I found it helpful the first couple of winters of full time bike commuting to keep a journal of the temperature when I left, what I decided to wear, and then anything that was uncomfortable when I got to my destination. Remember though, if you are dressed right you will be freezing for the first couple of miles.
Post Scripto: One should also note that what would be an unbearable cold and wet commute in the fall will be a rather pleasant shorts and t-shirt ride come spring. The body does remarkable things at adapting to cold and wet conditions over the course of the winter.
Last edited by bike2math; 08-20-07 at 09:33 AM.