I've had good luck with Rain-X here in Iowa. When I apply it, I clean the windshield thoroughly, apply the Rain-x, wait for it to "cloud", then buff it off. I do this while the car is in the Garage, out of direct sunlight, and I let it sit overnight.

I've heard good things about the additive for the windshield washers, but have never tried it. I don't use mine enough for it to probably be really effective..