Hi Peachy--This article recommends using newspaper to clean your windows and gives a simple green formula for window cleaner:
Care2 Greenliving :: Window-Cleaning Formula That Really Works
I've also seen recommendations for microfiber cloths. Quote from Wikipedia on microfiber cloths: "Microfibers are not made from a renewable resource and they are not biodegradable. However, the petroleum energy used in fertilizers, pesticides, transportation and processing to produce cotton and other renewable resource fibres may outweigh direct use of the petroleum as base stock for producing fibre."