Another exciting development in self-cleaning technology is based on what's known as "the lotus effect". See how water reacts to this lotus leaf?
That's because the lotus has a "superhydrophobic" surface. You see, when a drop of water hits a slanted surface, it will spread out and slowly slide off. But when a drop of water hits a slanted superhydrophobic surface, it actually retains its surface tension as a droplet and rolls off. As it rolls, if it happens to run across a particle of contamination (such as dirt), that particle will usually get taken along for the ride.
Watch this principle in action at the microscopic level:
This is the basic principle behind all sorts of new self-cleaning technologies, from glass to cars to walls. I can't find many superhydrophobic-based products that are actually out on the market yet, but there are plenty in the works. Here's one video that shows this principle in action: