SSBB ftw!!!
best game ever actually IMO

It would have to be Twilight Princess.. with SMG and SSBB right behind it.

I'm going to go left field here and say Wii sports. It's great with friends and it's just so damn playable. It's my most played game.

Zelda and Smash Brothers.

Smash Brothers is one of the best games on any platform.

SMG..

controls and it being Mario mkes it the best game

Brawl and RE4 so far. I know I'll be playing Brawl until the next Smash Bros comes out, but I've had a hankerin to go back and play RE4 yet again. I usually don't replay adventure games, but RE4 is too damn sweet. It was one of the best games to me last gen, and oddly enough, it might end up as one of the best for me this gen as well.

prolly Galaxy. Don't play it much though, its my sister's wii.

Super Smash Brothers. It will entertain me for years to come.

Super Smash Bros Brawl is basically top, however I rented Metroid Prime 3 and am still on the hunt for a reasonably priced copy, and I've also been quite impressed with what I've seen of No More Heroes.
There's also Mario Kart Wii coming up, which will probably give Brawl a run for its money.

Super Mario Galaxy