With all the recent rain thus far, I'm always looking for a safer way to maneuver through the sheets of wah-wah that smash against my Pinto.  Don't know yet if this the almighty answer to seeing better through the windshield, but it's worth a shot next time you are caught in a downpour.

Simple.  Make sure you have sunglasses in your vehicle.  When the torrential force of mother nature unleashes its full fury drastically dropping visibility, put on your sunglasses!  Of course, if you require regular specs to enhance your vision, I suggest using the either the "flip-down" or "lens attachment" model, so as not to impede your sight.

By doing this, you will still likely see the drops on the windshield, but not -- the sheet of rain!  This has been working for me, and since I have never been one to keep a secret, am passing a hopeful solution on to you-all.