I bought the Pirelli Sottozero II 235/40-18; 255/40-18 winter tires from Tire Rack to go on the stock 18" takeoffs that I bought from a fellow member here. I live in the Denver area and we get relatively frequent snows, but the roads are plowed right away and it usually clears in no more than two-days. I wanted a tire that would get me around in the snow and still be more than competent in the dry. This tire really fills the bill, giving me a very secure feeling on snow, ice, wet and dry. (My summer tires are the Michelin 19" PS2s).
BTW, Tire Rack's service was great, with quick turn around. Their recommended local installer "Swis Tire" had the most amazing installation equipment that I've seen, giving me the most secure feeling I've ever had with a tire-monkey handling expensive wheels and tires.