[Update: Note original image was for PDP's Wii aftermarket controller, not their upcoming design.]
The Wii U doesn't really have a good controller for fighting games, so enter PDP with their Wired Fight Pad as they're calling it. The controller has GameCube controller design inspirations, and is even licensed by Nintendo. It'll work for the Wii and Wii U, and plugs into the Wiimote.
The Fight Pad will run for $24.99, and is expected for release this holiday season. Any game that supports the Classic Controller and Classic Controller Pro will work with the Fight Pad, plus some Virtual Console games will work with this too. There will be multiple versions of the controller released as well, with designs featuring Mario, Yoshi, and Princess Peach.
Well Super Smash Bros. just got more enticing on the Wii U.