the best way i've found to clean glass is with plain water and two microfiber cloths. take the first, get it wet, and squeeze as much water as you can out of it. leave the second cloth dry. scrub down the window first with the damp cloth, and use the dry cloth to buff perfectly clean. the microfiber will absorb any grease or grime from the windows, without the use of chemicals or solvents.

you can buy these cloths online, or i've also seen them in the automotive section at wal-mart.

you have to be careful in washing these, in order to keep their absorbency. they must be washed alone (no cotton or other non-synthetic fabrics in the same wash load), and don't use fabric softener in the rinse or in the dryer.

i've never had truly clean windows until i started using these cloths. they're very easy to use, and worth every penny.

--dan.