While resistive touchscreens are being phased out in favor of capacitive screens, Carnegie Mellon University and Microsoft are working together on touchscreens for your body, called Skinput.
Sure, you could just get one of those laser keyboards and project it onto your arm, but Skinput actually recognizes which part of your body you've tapped, based on the sound that's made on either the skin, muscle or skeleton. The wearer must strap on an armband containing piezoelectric cantilevers, or sensors that measure pressure, acceleration and force, with a pico projector similar to what's found in phones beaming the interface onto the skin.
The technology could be used with gaming, or even pair up wirelessly to phones or PCs for a different form of input. I quite like the idea of texting just by dancing my fingers on my forearm, with the message sent by Bluetooth to the phone in my pocket—or taking my shoe off and beaming the keyboard and menu onto the sole, just like Maxwell Smart. [New Scientist]