Hmm... there are quite a few.
Some of my favorites are (excluding ones you already own):
Monster Hunter Tri
Super Smash Bros Brawl (a must have)
Xenoblade Chronicles
The Last Story
Little King's Story
Super Mario Galaxy 2 (if you liked the first one this one's even better)
Metroid Prime 3 (I'd recommend the Metroid Prime Trillogy Collection, but I think that was only being released for a limited time.)
New Super Mario Bros Wii
Mega Man 9 and 10 are available for download and those are pretty good
Muramasa: the Demon Blade (the artwork in this one is amazing)
There are some other good ones, but these are the absolute best. And that's not even counting all the great classic games you can download, along with lots of great GameCube titles which are compatible with the system.
Simskiller said:
Wii U is backwards compatible.
And of course there's this. But that's ignoring that it's not backwards compatible with the GameCube, so if you just get a Wii U without having either a GameCube or a Wii you're missing out on a lot of classic titles.