Scientists have developed a novel transparent touch screen interface dubbed LucidTouch.

This interesting user interface concept allows you to touch a display from behind. This avoids that your fingers obstruct the screen as it is the case with the iPhone or similar touch screen devices.

Mitsubishi Electric Research Laboratories and Microsoft Research constructed a prototype of this new touch screen concept.
It is still very far from production, but you can see a video on The NewScientist that shows the current prototype in action.