Bell Citi, same as summer, I just leave my rain cover on to cut down on the breeze. If it's < 32, I use a poly tube thingie from Nashbar pulled up over the back of my head. If it's < 20, I use a PSolarX HX balaclava (which is poly on top, polartec fleece on the bottom).

Last year I just duct taped the holes, and it was fine. But when ordering my rain gear last summer, I tossed in the rain cover for $10 and have been using that. It's yellow with reflective gunk so that's nice.