A safe and economical way to clean your windows is to use Vinegar. Mix 50/50 solution of Vinegar and Water. Yes sometimes vinegar can be pretty smelly at times but this will wear off pretty quickly and it will make your glass clear and streak free!
I perfer to use a squigee or newspaper rather than cloth or paper towel which they normally leave behind little pieces of fluff. With news paper you do not get little specs of fabric everywhere and it helps to get a streak free shine.