Laptop screen privacy filters not only keep prying eyes from seeing your laptop screen, but they also protect it from scratches. They are available in all the popular laptop sizes and are fairly inexpensive. Some are even reversible, with a glossy side and a matte side.
Laptop Screen Privacy Filter:
Laptop Screen Privacy Filter pictured: 3M Privacy Filter for 14.1 Inch Standard Laptop.
Laptop Screen Privacy Filter above: Akamai Office Products 14.0 Inch (Diagonally Measured) Privacy Screen for Widescreen Laptops (AP140W9B)