Oh, dear God. I bought winter tires (and knew I'd need them) before winter came in 2011. I recommend a winter LRR 15" tire because they're cheap (195/65R15). I bought Nokian Hakkapeliitta R's via ebay, but they weren't cheap. I would recommend Michelin ice Xi2/3 or something more affordable. Tirerack.com is your friend - you can also get rims (or steelies) and preview what they would look like on your car!
EDIT: Great, Nokian just released an "R2" - must... resist... (Don't worry - I'm not about to drop another couple hundred dollars on snow tires for the next like... 2 years)
2012 FF Ti HB Kona Blue, DCT, Built 5/24/2011, 401A + Ti Handling Package, Parking Technology Package, Winter Package, Moonroof, and MFT w/NAV at v3.6 115k miles and counting...