A new tablet prototype showed up last week at Ceatac Japan. Actually, there were probably several dozen, but this one stood out form the crowd. The Japanese telecom KDDI were showing off a new tablet that had the touch screen moved to the back of the device. There's no word on release date or price.
I don't think this is a practical design, actually. If the touchscreen is on the back, then you won't be able to lay the tablet down and use it. That really limits what you can do with it.