One cup of white vinegar to four cups of water (for a stronger solution, one cup of white vinegar to one cup of water works) makes a fine window-washing fluid, substituting for Windex. If windows appear streaky after washing with vinegar, add a half-teaspoon of liquid soap to the mix. This removes the waxy, streak-causing residue left over by commercial window cleaners.
Malt vinegar sprinkled onto crumpled newspaper is a traditional, and still-popular, method of cleaning grease-smeared windows and mirrors in the UK.
from wikipedia