John:
I've fished in weather as cold as -7F. Keeping your hands warm, while retaining the ability to fish, is a real challenge. I tried ski gloves, mittens and even the neoprene gloves (which are fine for wade fishing in cold streams, but my hands would perspire and if the gloves are too tight, they can cut your circulation off to your fingers).
My solution is two fold: I have a pair of Cabela's fleece gloves with neoprene palms and slit fingers for my index finger and my thumb. I can fold back the tips and velcro them in place to tie knots or thread leaders. The gloves are black, comfortable and UNBELIEVABLY warm for how thin they are. There is also a velcro strap across the wrist to keep them tight.
If its too cold even for these gloves, I have an oversize pair of wool, fingerless gloves that I will pull on over the fleece gloves. The tips of my fingers may get a bit cold, but the rest of my hand stays nice and toasty.
I can also just fish with the fingerless wool gloves if the fleece gloves are overkill.