A base layer is a key part of your arsenal when you prepare yourself for a day of winter adventure.  Choose wisely.  Lot's of brands sell base layers.  The basic rule of thumb is that you don't want that old cotton t-shirt your wife wanted you to throw out last year to be your base layer.  Toss the t-shirt or use it to work on your bike.  You need the real stuff.  Capilene base layer by Patagonia is a great buy right now.  Patagonia is upgrading it's base layer to include three levels of capilene 1,2, and 3.  This means substantial savings on older versions of their performance base layer.  Take advantage of T-shirt prices on the one layer that you never take off- and the one that hugs your skin.
    Other base layers that you will want to consider are Burton's first layer, the North Face base layer, Under Armor, and CWX.  These fabrics are often light enough to be washed in a sink basin and will dry in a twenty four hour period.  Three sets on a week long trip is luxury, but you can get by on two sets and one set for the spartan ultralight traveler.
    Also worthy of note-when your base layer has reached holy status and your wife is begging you to throw it out- it can be recycled.  Patagonia has a capilene recycling program.  It's part of their environmental initiative that includes reimbursing employees for riding bikes or electric cars to work, making fleece outerwear out of plastic soda bottles, and using 100% organic cotton for all their cotton needs.  To participate in the capilene recycling program-drop off your clean, spent, capilene duds at your local Patagonia store or send them here:
       Patagonia Service Center
      Attention: Common Threads Recycling Program
      8550 White Fir Street
      Reno, Nevada 89523-8939