Burton Outlast Midweight Thermal Crew
Pros: Good length in body and arms so that you don't have to worry about snow trying to get in there. Lightweight enough to act as your bottom layer and then to add a couple more if needed.
Other Thoughts: Cute design on the front so you don't have to worry about sporting your thermals around town after a long day of riding. The Outlast thermal is warm and will keep you feeling dry and comfortable all day long.