E3 Console Post #2: Wii MotionPlusFrom 1UP:
Nintendo has just announced the Wii MotionPlus, a plug-in adapter for the Wiimote that, as Nintendo describes it, can more quickly and accurately reflecting motions in a 3-D space.
Microsoft is widely expected to announce a motion controller at their E3 presentation (later today), so it looks like Nintendo wanted to strike first. There's a picture at the link, and the adapter looks like a two-inch extension that plugs into the bottom of the Wiimote. Very clean design.
Presumably, this adds an additional acceleration sensor for more precise motion tracking.