Let's see.
MadWorld (if you hate violent games, this one's not for you. But it's pretty cool)
Arc Rise Fantasia
Rune Factory: Frontier (I freaking LOVE this game)
Zack & Wiki
Muramasa: The Demon Blade
The Last Story
Spyborgs
Rayman Origins
Trauma Team
Resident Evil 4 (best version of RE4 available)
Resident Evil: Darkside Chronicles
Monster Hunter 3 (although I don't think you can play online on it anymore)
Klonoa
New Super Mario Bros.
Both No More Heroes games
Okami
Kirby Collection
House of the Dead: Overkill
Res Steel 2
Mario Kart Wii
Mario Tennis
Kirby: Return to Dream Land
Super Paper Mario
Sengoku Basara: Samurai Heroes
I honestly cannot recommend Xenoblade Chronicles myself. I smurfing hated it, but everyone else and their mom seems to have liked it so try it too, I suppose.
Here's some cool Gamecube stuff too (I don't know if you got a regular Wii or the Family Edition that can't play GC stuff):
Gotcha Force
Tales of Symphonia
Sonic Gems Collection
Viewtiful Joe 1 and 2
PK: Out of the Shadows
Cubivore
F-Zero GX
Also, I highly recommend the Phoenix Wright games if you are able to use your Wii online and have never played them before. They have them on the Nintendo e-shop or whatever it's called. They only have up to Trials and Tribulations, though (the 3rd game).