I have a pair of black shooting mitts and the palm is slashed and held closed by a velcro tab. Their initial purpose is for hunting howvere find that they workk great in cold weather. They are a bit on the bulky side but if my fingers get too warm, it's just a matter of opening the palm portion for a few minutes to get the temp. back to normal.
I have found neoprene fishing gloves to provide great warmth when it gets in the 20s. The palms and insides of the fingers are rubber and creat a great gripping surface.
I agree with ir.
I love the neoprene goves because I can actually lock up my bike with them on. The problem with them is that you can get cold fast if you let your hands sweat in them. They don't extract poisture well. Still nice to have.
I also like leather combat gloves. I wore combat gloves at -29oC once with a couple wool sox over them and managed to stay toasty quite well.