In addition to Windex there are a few other options. You can always try using Simple Green followed by Windex, just be careful to keep it off the paint.

1) Bon Ami (the household cleaner) is also supposed to work well on windshields. I'd test it on a corner first to make sure though.

2) Pep Boys or your local auto store should have some specialized windshield cleaner. It goes on like a paste, buffs around, then is hosed off.

3) Old fashioned toothpaste. Be sure to get paste not gel. Apply, buff, hose off.

Keep any and all of those off the paint as they are much too aggressive for clearcoat. Give those a try on the glass and let us know how they worked for you.

Hope this helps...Lee