I've run Pirelli Scorpion Zero Asimmetricos the last few years with great luck. They get me through the few measurable snows that hit the midwest each winter. Coming from Diamaris, the Pirellis don't give up any dry or wet weather performance and they definitely wear more evenly and last longer. If you want to run staggered 19's year-round, give them a look.
pretty badass tread design also. Power is Nothing Without Control
$888 for a set on TireRack
on a side note, has anyone here put Hankooks on their X? a Korean tire on a BMW just doesn't seem right...