What is a good shampoo to smooth frizzy hair?

I have naturally frizzy hair. When I dry it straight, it is thick and kind of wants to tangle. It looks good after I flight iron it.....for about an hour LoL. As soon as I get hot, get in humidity, or in wind, it frizzes. It doens't frizz as bad as when I first dry it, but it does get frizzy. What is a good shampoo that relaxes frizzy hair?