This...
I just suck it up and fish. I duck hunt without gloves so fishing is usually drier, hence warmer.
If I use anything it is the thermax gloves mentioned earlier.

This

Hands down, go to an army surplus, get the 100% wool glove inserts, they even have ones with the fingertips already cut out. You never have to remove them. They insulate just as well wet as dry. You can land fish, get in you live well, fish in rain, never needing to remove them. I wear mine even on cool mornings just to have warm hands on a cool morning. Get an extra pair, your partner will pay dearly for them on a cold morning! Nothing synthetic works as well as wool. Latex will hake your hands sweat, they'll be colder than with nothing on afterwards.

Simms fingerless with fold over mit.They have sloto to drop handwarmer packets in at the wrist. Keeps my hands warm when fishing. I flip the mitts over while running. The packets sit on your radial artery which helps blood flow and keeping your fingers from going numb

I bought a pair of Sealskinz gloves that work awesome! They are warm and waterproof so you can reach in the water and lip a fish if need be. They don't breathe well so I don't wear them unless it's real cold outside. Good luck!

I put on thin cotton glove liners.
Then I put Black latex gloves over them.
That keeps the water off the cotton liner from my thumb I keep on the spool.
Use black latex. If some sun is out it will heat the black gloves.
Keeping the cold wind and water off your hands helps a lot.
I buy a box of 100 at O"reilys auto.

Why latex gloves under your gloves? Why is that so effective?

I have some cabelas neoprene gloves that have fleece inside. They work while still being able to cast. You're not going to be toasty, but you'll have feeling

I wear a mitten style glove that I bought at Walmart and these are by far the warmest thing I've even put on my hands. I worked in refrigerated environments where it was really cold for years and I duck hunt and do that usually in the coldest part of the season, many times when there is ice on the water; and I have tried everything. These style of gloves get it done. Two things I think that make them work so well is the fact your fingers can share heat where they can't with regular gloves and they also allow for more blood flow...... I've been out in weather in the teens and as long as I kept my fingers covered with the mittens my hands where very comfortably warm. I usually keep my right hand uncovered while hunting but will slip the mitten back over it when I get cold. These aren't exactly what I have but are the closest thing I can find.....also when you buy gloves, looser is better, air space creates insulation and promotes blood flow....
http://www.basspro.com/RedHead-Convertible-Gloves/product/1412201136314/

The latex gloves make me sweat and then my hands are cold. Am I the only one?

I go full electric ski gloves.

Here's a picture from Sunday..... It was brutal!

Buy a Buddy Heater.