Change it up. If you part your hair on the left, part it on the right. Usually, it'll show cleaner hair, and it will create the illusion of more volume. Plus, you get that hair-in-the-eyes '90s shoegazer look, which is sexy.
Learn to love scarves. And headbands. And anything else that lets you get your hair away from your face. It's an obvious solution, but it works.
Do the twist. If your hair is long enough, twist or braid an inch-wide section of hair on each side of your face. Pull those back, and they'll look sleek. That distracts from the slick.
For another trio of tips, read more.
Wash what you can. If you have bangs, washing those can give you a fresher look.
Use a dry shampoo. Truth be told, it isn't the perfect solution, but dry shampoos can soak up grease. Apply them close to the scalp, and use less than you think you'll need. Oscar Blandi's version ($11-19) adds a fresh scent, but it's sometimes visible on medium-to-dark hair. Bumble and bumble's powder ($19-35) comes in different shades, so it may match better. In a pinch, you can use baby powder, too.
Wipe out. If you can't shampoo your hair, you can still give it a quick cleaning. Ted Gibson Hair Sheets ($17.50) are made to do just that. Conversely, a sulfate-free baby wipe such as Avalon Baby Wipes ($6.39) can gently refresh, too.
Source: Flickr User me and the sysop