fall/spring lite winter pants
Here are a few decent pants for cold commuter riding that are on sale. They are not for the dead of winter. In the mid atlantic area these are great for most but not all of the winter commuting season. I like pants that I can wear on the train, at work etc.. I wear tights but don't always like to change at work.
At REI: http://tinyurl.com/b6p7x
There's a $20 and $30 coupon if you spend 100-150
At Sierra: http://tinyurl.com/8rbfk
Sporthill makes some good stuff. Their best winter pants are the XC which are too hot most of the times. The 2 that I listed are good for the 30F-60F.