Meguiars Glass Polishing Compound is a great product for cleaning / polishing windows. It cleanses the glass at the bottom and can in some cases remove small micro -rides, and restore great clarity and depth in the pane.
Note that there is abrasive in the product, so it must not be used on top of solar film and the like.
You can very well use Meguiars Glass Sealant after treatment with this product to give your windows a good water repellent effect, for daily cleaning of the windows we recommend Meguiars Perfect Clarity Glass Cleaner.