My approach to windshield cleaning is very simple. I use plain tap water -- warm. I wipe with a damp wash cloth (almost dripping), wipe once with a dry terry cloth towel, and then buff completely dry with a second terry cloth towel.
No more glass cleaner for me since both of my previous favorites (Meguire's Final Inspection and Cinch Window cleaner) starting streaking. Every couple weeks I apply Rain-X, using a paper towel to remove the haze, and then the above method to polish the windows clean.
I even carry a damp cloth, in a zip-lock baggie, in my detailing bag to clear the bugs and road spray I frequently get during my hour-long commute (which always seems to be directly into the sun.) I hate dirty, streaky windows! I sometimes wonder how the person in the car in front of me can see out their windshield. They probably can't.
Gregg
2001 Proton Yellow #1379