Lots has been said. More than I can say, and probably better as well. I'd just like to point out that the families of military members, while not in the line of fire, still bear an incredible burden along with that vet. So if you're out and about, and you feel like thanking a vet, make sure to include their spouse in with that.
God knows my wife has put up with more crap than she ever thought possible as she supported me.