Xenon has just started selling a futuristic USB recharging cable for iPad, iPhone, and iPod, which not only lights up, but you can see how fast your device is recharging by how fast the light pulses along the cable. And when your charge is full, the light turns off.
More specifically, the speed of the light pulses reflects the charge capacity of the device at the moment. So it pulses quickly at first, slows down as the devices charges, and finally goes dark. Visually very cool to have in a dark room while your device charges, and informative, too.
source: Impress (Japanese)