As the person who sees his scalp the most, I can vouch for the efficacy of the prescription shampoo; Nizoral, unlike most dandruff shampoos, is an antifungal and therefore helps with dandruff that isn't just dry skin.

I have dry skin everywhere, myself, so I use the same remedy on my scalp that I do on the rest of my skin: moisturizer, in this case a good clean-rinsing conditioner. Cutting my hair short, keeping it that way (4 inches is long enough to make my scalp sweat then flake), and washing it every other day also keeps down the dandruff.