i have found that AG Fast Glass does a fantastic job on my car...lasts weeks too. noticed on friday when we had a lot of rain i was intermittent much of the time whilst other cars wipers were going furiously!
I use fast glass but that's only a cleaner as far as im aware.
I'm going to look into carlack or gtechniq stuff - some kind of glass sealant either way. The other issue is that dirt on the glass seems to stop water gliding off so regular snowfoam and wash is also recommended.
Yup my car wash process is:
Rinse with Pressure washer to get any large bits of dirt/heavy build up off
Wheels Cleaned with Bilbery Wheel cleaner
Snowfoam and leave for 5-10 mins
Rinse
Snowfoam for 5 mins again and then wash using the 2BM with a wash mit. I also use one of those windscreen sponges to get rid of any fly deposits etc
Rinse
Dry
Clean all glass with fast glass, AG Glass polish and then apply Rain-X to windscreen, front side windows and rear screen.
Use Megs Spray Quick Wax & Speed detailer to keep on top of shine
Once every 2-3 months the wheels come off and the car gets a proper waxing