read somewhere that scientists are developing 'visual stealth' technology - current tech is mostly radio and radar stealth.
hundred of mini digital cameras would be situated across an object, which is covered in a cold plasma incandescent alloy. The cameras would capture the environment around the object and project a 'camo' imagery across the plasma skin, thereby rendering it 'invisible' to all but the most observant.
unfortunately, this may not really work for airplanes due to the heat signature of the jetstreams and the speed at which the plane moves means that the processors managing the camo image would have to be close to a supercomputer 3 x the size of the plane...
but wouldn't it cool.... :P