Let me second the recommendation of the Michelin X-Ice tire, and also emphasize that you need FOUR winter tires.
While other winter tires may approach (but not exceed) the traction of the X-ice, none exceed its long tread life, thus making it more economical in the long run. It also provides an excellent ride, dry road handling characteristics that are far superior to most winter tires, and a noise level that is lower than that of most winter tires.