From a former technician working on portable computers:
DO NOT USE WINDEX!!! DO NOT USE ANYTHING WITH AMMONIA IN IT!!!
Many LCD displays, while having a glass panel in them, also have a light plastic coating. Ammonia will melt this, causing the display to become cloudy. It will also VOID your WARRANTY on the LCD.
DO NOT USE WINDEX!!!
Mostly, I'd just use a soft cloth, with gentle pressure to rub out light marks. And for God's sake, DON'T TOUCH IT WITH YOUR DAMN FINGERS. It's a display, not a touchpad! Keep it from getting spotted up in the first place! (finger marks on monitors - one of my pet peeves)
Some stores like Office Depot or the like, will have LCD cleaning solutions specially formulated for laptop and LCD monitors. I would ONLY use something that SPECIFICALLY states it is OK to use on LCD displays.