Although not explicitly showcased as part of its E3 pre-show press conference today, Nintendo has released pictures of the legacy 'classic' controller for the Nintendo Wii as part of its E3 press kit.
This is an optional peripheral add-on which will make it straightforward to play GameCube titles and other classic Wii-compatible games which use conventional control layouts - it's unclear whether it can also be used to play some Wii titles if desired.
The controller includes a D-pad, two analog sticks, four face buttons (labeled X, Y, B, and A) and Select, Home, and Start buttons in a similar way to the Wii. In addition, there appear to be a total of four shoulder buttons, including two in the conventional L and R positions and two closer to the center of the controller.
Nintendo has not yet commented on the pricing or availability of this controller. But it's presumed that it will debut alongside the Wii at launch, and be particularly useful when playing games with the Virtual Console service, since it perhaps most resembles a Super Nintendo controller in terms of form.