You can buy commercial cleaners, but you can make your own for a fraction. A 50/50 mixture of isopropyl alcohol and water is used to clean your screen. Look for a 90% or higher pure isopropyl alcohol at your local drug store.
Don't clean your screen too often. To minimize the time between cleaners, use compressed air or a soft cloth to remove dust. Your screen should not have to be cleaned more than once every 3 to 6 months.