I can't stand having cold hands, and gladly chose form over function to keep them warm
at 30 degrees I switch over to these military surplus trigger finger mittens
http://www.surplusnation.com/product...ittens-w-liner
at 20 degees I throw one of these into each of them
http://www.amazon.com/Hand-Warmers-H...YXE/ref=sr_1_9
(cheap copies vailable on eBay)
It's really true that a mitten is essential for warm hands, your fingers will keep each other warm if they can touch. I'm sure several of the other mittens in this thread will work equally well, I like mine because
A) I can slip my index finger into the trigger part when I need to do a bunch of shifting
B) They are big enough to fit a heater into when its really cold