A 50:50 solution of vinegar and water will leave your windows spanking clean.
Most professional window cleaners swear by cool, clean water to wash windows.
In Enid Blyton's The Mystery of the Holly Lane, the Five Find-outers and the Dog stumble upon a mystery when Larry engages in window cleaning for a spot of fun.
Club soda or a solution of baking soda and water work well as window cleaners.