The guys at Instructables have created a cool privacy monitor based on a modified LCD display. The monitor appears to be completely white until the user puts on 3D glasses.
Privacy LCD monitor
You can probably find better uses for your monitor but this modified LCD monitor is actually an interesting design. The monitor ensures privacy from co-workers, friends, wives etc. if you need that kind of thing.
The modified 3D monitor only shows pictures through the glasses
The guys at Instructables have opened a LCD monitor, removed the polarization filter and removed the adhesive film with paint thinner. They then reassembled the monitor and put the polarization filter into the 3D glasses.
The result is a monitor that looks like it is broken at first glance but shows you the correct image when the glasses are worn. See this video for a demonstration.