Vinegar and Water
I have been really pleased with the glass cleaner I normally use, Odoban's Glass Control, which I pick up at Home Depot. It's supposed to be more environmentally friendly than other products, and I think it cleans better (ie. less streaks) than other brands. Recently I've been reading about home made cleaners and thought I'd try to make my own glass cleaner since I just ran out. It couldn't be easier to make, and it was certainly easier to whip this together than to haul the kids to HD. All it takes is just one part water, one part white vinegar.
After cleaning the glass furniture downstairs, I'm surprised at how well it cleaned without streaks. The vinegar smell was hard for me to get over at first, but then I figured it was better to have a smell from a natural product rather than a fake smell from a product, because what you're really smelling are chemicals.
I'm sticking with the vinegar and water method, as it's natural, works just as well (if not better), and it's cheaper. Guess I need to put more vinegar on the grocery list!