Vinegar also helps with soap residue that comes with natural soap based shampoos as well. Apple cider vinegar is the usual thing to use. If you're in the sun it will give your hair a reddish tint that's very nice. If you prefer blonde with no red overtones, then lemon juice is what you want.
One of the truly natural shampoos I've found is Tate's. It leaves no residue at all and there is nothing questionable in it at all. It's pricey but it's really concentrated. Not too many health food stores here carry it, but it can be found on the Internet.
A small bottle lasts me and my daughter for a couple of months, and we both have waist+ length hair.
Tate's sells a conditioner too, but I've never used it. I mostly brush my hair properly to keep the tangles away, though olive oil can help if you're having particular problems. You can do a hot oil treatment or you can put a few drops on your brush and brush 100 strokes at least before you go to bed (grandma's old trick, that last one is).