The most obvious, I think, is yet another screen for multiplayer. Three players each with their own screen, or up to six players total (assuming the Wii U can handle that).
Mario Kart U is likely going to support two gamepads, because once it becomes standard, then all the major titles will be supporting it. Maybe you could have two players each playing on a gamepad while the tv shows a more cinematic view of the race. Similar to what the camera does after you beat a race. It would be entertaining for people who aren't playing the game.
Smash Bros. U, perhaps players playing on the gamepad could have a more zoomed in view of their character so they don't get lost. Especially if Smash Bros. U adds in more than 4 players per battle. Or bring back the camera mode from Melee and the person using the gamepad can like get up and walk around the room as if they had a camera and were trying to get a good picture of the fight. So the view would change depending on where they were in relation to the tv and what angle they held it at.
Co-Op RPG. Each player would easily be able to access their inventory without the other character having to pause. Like Crystal Chronicles on the gamcube.
I'm sure Nintendo is going to come up with a new game, similar to Wii Play, that will introduce us to the uses of the second game pad, much as Nintendo Land has introduced to us the use of one gamepad. I'm not sure if it's going to be a Wii Sports U or Wii Play U, but I'm looking forward to whatever Nintendo comes up with. Maybe even a Nintendo Land 2, huh?
Well, what do you guys think?

