Hi,
I use Nizoral. You can get it at any drugstore. It is a shampoo, and it can dry out your hair, so make sure to DC afterwards. Once you use it for 4 or 5 shampoos, you can cut it down to every fifth shampoo or so. This is the only thign I've found that works. It contains an anti-fungal, since many true dandruffs are caused by a fungus. It COULD just be a flaky scalp in reaction to dryness, or even an allergy to something you are using or eating.
Good luck!