I really like convertible glove/mittens. I have two pairs now. I like being able to open the flap if my hands get too warm or I need to tinker with the bike.

I have a knit pair that I picked up at Kohls a couple of years ago. As long as it's not raining, they work for me down into the upper 20's. I also got a pair of these recently:

http://www.amazon.com/Man*****-Casca.../dp/B000O5WN3S

I imagine I could wear them at the north pole in the dead of winter and have warm hands. YMMV of course.