There is actually an amazing product out there for oily hair. I can also tell you where to purchase this item as well. Crome has a great shampoo and conditioner for oily hair. It really works wonders, and you can purchase it at any Planet Beauty store. Most high end salons carry this brand as well, if you do not have a Planet Beauty in your area.
Well you probably need to use a clarifying shampoo.... Paul Mitchel makes 3 different ones called shampoo 1,2 or 3. As a hair dresser I would never recommend dawn dish soap but I have heard that works too. But think about it.... There's a reason why it's just meant for your dishes and not your hair.