Wii Sports was definitely the star of the show on Wii, and arguably the biggest killer app ever.
I do feel like there were other games that moved a lot of Wiis though; NSMBWii as the first new 2D Mario on consoles in nearly two decades, Mario Kart as one of the ultimate party games, Smash, Wii Fit, to a lesser extent Twilight Princess which was the main reason to buy it early on if you weren't into the more casual stuff.