Try a clarifying shampoo or one that has salicylic acid as one of the ingredients like dandruff shampoo, or use a small amount of vinegar in your rinse water, just to give it a really thorough clean & get rid of any build up. Also, if you brush just before you wash, that helps get the scalp clean. Massage the shampoo into your scalp, shampoo twice, and if you use conditioner, only on the ends.

I've been having oiliness issues lately too. I've taken to wiping my face sometimes during the day with witchhazel, it seems to cut through the grease without drying or stimulating more oil. And I love love clay masques, my skin is much better for a few days after using them, but I don't do them often enough.

You can also try sleeping with a clean towel over your pillowcase (it soaks up some of the oil while you sleep), and I've also heard of people brushing baby powder or cornstarch into their hair, it helps absorb the oil.