I guess technically you could add Windex to your washer fluid reservoir, but I wouldn't do that. Any of that standard blue washer stuff you get at a gas station or auto parts store is good, it's only a dollar or two. If you really want to spend some money, then you can buy some washer fluid from the dealer.
Has anyone used Rain-X that also has the cold weather package with headlight washers? I've used the Rain-X fluid in previous vehicles and LOVED the stuff, but I'm concerned with the quantity that will end up on my paint when the headlight washers activate (and any ill effects that the stuff will have on the paint).