Straight from Dell.
http://support.dell.com/support/topics/global.aspx/support/dsn/en/document?c=us&dl=false&l=en&s=gen&docid=DFCC6A44B2374EF6B398593361662C3B&doclang=en
Do not use any of the following chemicals or any solutions that contain them: Acetone, ethyl alcohol, toluene, ethyl acid, ammonia, or methyl chloride. If you have a different chemical or solution and are not sure whether it is suitable, do not use it. Using any of the chemicals in the previous list may cause permanent damage to the LCD screen. Some commercial window cleaners contain ammonia and are, therefore, unacceptable.