You might have Seborrhea Dermatitis, or something similar. I have that on my scalp and parts of my face.
Anyway, something like Denorex with coal tar or salicylic acid is good for when you're having a flare. Head and Shoulders Intensive care for the everyday shampoo. Also use some sort of moisturizing conditioner. Occasionally rotate shampoo brands.
After your shower, don't be afraid to try to work in some sort of lotion. CeraVe is the latest stuff my dermatologist has recommended to me. It seems to work really well.
Beyond that, my dermatologist has prescribed topical ointments and hair moose for when I can't get flares under control, and a ketoconazole shampoo to use a couple times per week prophylactically.