What Type of Cleaner is good for window cleaning?
Typically, window cleaners use dish soap (Palmolive, Dawn, Joy etc). The purpose of soap is to remove the friction between the squeegee blade and the window. It also helps with visibility between areas cleaned and uncleaned. There are other "specialty soap" that are available on the market, but nothing works as good as good ol' dish soap.
Pro tip: Too much soap will make water dry faster, especially in direct sun light.