I live in Maine and commute year round, 12 miles round trip.
The only cycle-specific clothing that I own:
J & G waterproof breathable jacket
cycling gloves
helmet
Rainmates

In the winter I wear a wool base layer, regular work clothes, waterproof steel toe shoes (required for work) wool socks, wind & waterproof gloves, balaclava (extreme cold) my J & G jacket, and my Rainmates. I taped the vents on my helmet for use in the winter.

This set up works for my commute, down to about -20 Fahrenheit.