Wii sports doesn't go online unfortunately. I'm sure the sequel probably will.
My recommendations (just purely personal taste)
-Twilight Princess
-Metroid Prime 3: Corruption
-Mario Galaxy
-Super Paper Mario
-Smash Bros. Brawl
-Guitar Hero III
-No More Heroes
-Zack & Wiki
They are all great games and give you a variety of genres to choose from. The last two on my list are kinda hit and miss for some people. No More Heroes in an M-rated action game, it's very stylish and bloody, from the same people who made Killer 7 a couple years ago. Totally unique experience, one of the most original games I've played lately. Zack and Wiki is a point and click adventure puzzler like those old computer games where you pick up random objects and use them to progress through levels.
There's also a lot of older games that were redone for the Wii in case you missed it. Like Resident Evil 4, Okami (really overlooked gem), and Bully. As always you can just YouTube the games and check out some gameplay videos to see if you like any of the ones I mentioned.