I bought some military surplus wool gloves...one pair with fingers and one pair fingerless. They fit either hand, so I take one glove from each pair and PRESTO, I have one glove with fingers for my bow hand and one fingerless for my string hand (I shoot a tab), plus I have an extra pair. I bought both pair for ten bucks at a Wisconsin hardware store. With those on, my hands have been warm and comfortable down to 25 degrees (coldest I've used them in). If the fingers on my string hand get a little chilly, I just put my hand in the pocket of my wool coat or vest.
May not be the best option out there, but it's the best I've found since I started shooting a tab. Not to mention, the price is right.