Nothing. I applied this to my D60 when I got it Way Back When and the display's still in great shape, although the bottom edge of the camera's showing some wear. If you desperately feel the need to put something on there, you can get several rolls of Bob Gross' clear packaging tape for the price of almost any of the suggested photo- or PDA- specific alternatives and be set for a lifetime or until they come up with 4" display screens.

