I offer a slight variation on the pp's suggestions. To get off the heavy stuff, a sponge and bucket of 1/4 cup washing soda: 2 cups white vinegar: 6 cups water. (It will bubble a bit, but that's normal and will stop after a few seconds.) Then, go back for a final cleaning with a 50/50 mix of vinegar and water.
I don't use microfiber cloths when I'm doing all my windows at once - I don't have enough of them. Old cotton dishtowels, washcloths, and tee shirts do nicely.