You can also try household "Bon Ami" or toothpaste (paste, not gel) for windshield treatments. As Andras noted, do NOT let these get on the paint. If the do, rinse thoroughly with water, then wash gently. A good time to do the windshield treatment is right before you wash the rest of the car. Clean the windshield with something like Windex, then do the BonAmi/Pumice/toothpaste treatment, then rinse/wash the car as normal. Following all that up you may want to try a windshield treatment like STP Vision Blade. I've used that before and it really seems to help night rain visibilty by cutting down on streaking and whatnot. Lasts about 4-6 months too which isn't bad for $20 or so bucks and 15 mins of labor.

Hope this helps...Lee