Resident Evil 4 is a great deal for $30.00
My favorite right now is Excite Truck. It's a racing game that's arcade style, you take a off road truck and you just drive all kinds of crazy.
Wario ware is an awesome mini game, game. It's got all these crazy weird things you do with the wii remote. Probably the weirdest game on the system but maybe one of the funnest.
Rayman Raggin Rabbids is also a fun mini game series.
But before you make a $50.00 mistake, rent the game. especialy with the wii control style.