I REALLY like the Dunlop Wintersport 3D's. I have been using them for years. First on my E46 now on my E90 ///M3.
He is a picture of me testing them for the first time with my E90 during the "freak" snow we received last week in NJ:
It was loads of fun, and they handled nearly as good on the snow as my summer's do on dry tarmac. Amazing grip.