The US military is reportedly experimenting with a weapon that can cause people to experience extreme pain. The projectile-styled device is said to fire a laser pulse that generates a burst of expanding plasma. According to an article(1) in New Scientist, it's planned for use in 2007, and "could literally knock rioters off their feet."

1. http://www.newscientist.com/channel/mech-tech/mg18524894.500