Dandruff is the result of a scalp too oily, not because it's dry. Maybe you are using the wrong shampoo. Use the shampoo that is especially made for your kind of hair/ scalp.
Head&Shoulders has about 6 new shampoos out and one of them is exactly for frizz control. I don't have a dandruff problem but I do use the conditioning one because it smells really fresh and clean. There isn't any residue from it and it makes my hair silky and shiny. I choose the one with the pink cap and it says conditioning on the label. I use other shampoos too and switch it up, so they all continue to work.
Now they have added 3 more, and changed the look of the bottle [Only registered and activated users can see links. ]
It takes awhile to load but it's worth it and there is a coupon for you in the body of it.