Rain-X
I was happy to learn the 737-800 had a permenant rain repellent coating built into the windshield. My company deactivated the rain-repellent system on all our planes for environmental reasons. I miss it. I've found Boeing's rain repellent coating useless. Anyone else?
However, I've recently been trying out Rain-X. I've flight tested it, 5 hours at .82 mach, landed in heavy rain without ever turning on the wipers! That was awesome! I picked the runway up clearly at 1000 feet, the other guy had to watch a "slide-show" presentation of the approach, as his windscreen filled with water and got wiped away. My side of the cokpit was nice and quite, his sounded like someone kicking a trash can.
Give it a try, it's worth the lean out the window to do it.