I'm in Chicago and use just one set of tires year round, have had them for the past 2 winters, General Exclaim UHP XL tires on ASA AR1 wheels, rear 19" by 9.5" with 265/30WR-19 tires, front 19 x 8.5" with 235/35WR-19 tires, bought the entire set up from tirerack.com for $1550 shipped. At the time I bought them they were rated number 1 out of 46 tires in customer surveys on the site and the only tire in that size with an M+S (mud and snow) rating. They're passable in the winter and great in summer. With more than 4" snow on ground it's tough going though. Less than 4" I can get anywhere, still gotta be gentle on the gas, could even make it up and down my driveway, which was impossible with the stock runflats in ANY snow. Of course they're not as good as dedicated snow tires, which I had on my old Mazda RX8, but good enough that I don't have a need for a separate set and do the changeover twice a year. Thread with pics of my setup:
http://www.e90post.com/forums/showthread.php?t=23392