I'm assuming U have "oily" hair. There's plenty of great shampoos that work great for "oily" hair, shop around and experiment. As for "greasy" hair, (why U would have grease in your hair is beyond me), use Dawn dishwashing liquid.
a good question, but lacking some information. age, nationality, course or fine hair, curly or straight, long or short, color treated or permed will all make a difference in how best to care for your hair.