Mine would be:
1. Super Mario Galaxy
2. Super Smash Bros Brawl
3. Metroid Prime 3: Corruption
4. Mario Kart Wii
5. Wii Sports
Honorable mention: No More Heroes
The Legend of Zelda: Twilight Princess and Resident Evil 4 would be on there, but I had them for Gamecube and personally think of them as more of Gamecube games.