A new Japanese import for the Nintendo DS, Slide Adventure: Mag Kid, comes with a never-before-seen peripheral called the Slide Controller—converting the DS into a sort of optical mouse.
Interfacing through the large, generally unused GBA port, the Slide Controller allows you to move the DS around on a flat surface, just like a mouse. The game then registers the controls and responds accordingly (it has something to do with robots, magnetism, and we're sure, the end of the world).
We're excited about the peripheral for other prospects—like the simulation of a magnifying glass or—we're actually out of ideas. Still, adding a screen to a mouse with 1:1 controls is brilliant. But adding a mouse to a screen of the DS could be genius...assuming there are at least a couple of decent titles.