I have several games for the Wii. My favorite:
Super Paper Mario
Excite Truck (seriously underrated - a lot of fun, arcady type of racing)
Wii Sports (great for parties)
Wario is a quirky little game that seems to be more like a gimmick with the Wii Remote than anything else.
My kids love to play their GameCube games on the Wii with the Wavebird Wireless Controllers. They're switching back and forth between the Virtual Console games I downloaded, GameCube games (Mario Kart, NHL Blitz, Sega Soccer Slam), and the Wii games. It's really a great system for us.
I also want to get Elebits - supposed to be very good.