Not long ago it seems there was a fair bit of buzz over PDP's announcement of a licensed GameCube-inspired Fight Pad for Wii and Wii U, which is all set to be shown in some form during E3. If you're a fan of the existing Wii U Pro Controller but want a more interesting design, however, a custom range from Evil Controllers may be what you're looking for.
Available in four designs, these most certainly aren't officially licensed, but nevertheless look rather nice. They're actually customised shells over official Wii U Pro Controllers, so in theory the pad should be of a high quality as per Nintendo's standard option; naturally the quality of the custom job is down to the seller. These come at a bit of a premium, too, costing $79.99 in the US, when you can typically get the official version from a major retailer for $49.99, and cheaper if you shop around.
Are these designs nifty enough to justify the extra cost? That's for you and other Wii U owners to decide.