I commute throughout the winter here in northeast PA as long as the roads are free of snow/ice. I wear leather overpants and a leather (nonperfed) jacket. I have leather Goretex boots, a Shampa Tall Deck dickie, and Gerbings gloves. I then try to wear a long sleeve shirt underneath of it. This gets me by for my half hour highway commute so far down into the low single digits (Fahrenheit).
The only two things that I feel are necessities in really cold weather are my double-paned helmet visor and heated gloves. This keeps my fingers warm and able to safely use the hand controls, and lets me see without a frosted visor. As long as I've got those two things, I'm good to go for my commute.
My current setup leaves me pretty cold when I get to my destination, but for a half-hour commute, it's fine. If I were to go any further in temps colder than say 20 degrees F, I'd need to figure out something a bit better.