Gamestop is running a little sale, at least until August 2nd.  A variety of new games are on sale for just $20, including these Mario-related Wii titles:

New Play Control! Donkey Kong Jungle Beat
Mario & Sonic at the Olympic Games
Wario Land: Shake It

In addition, the following Wii titles are also on sale for $20 (as are a variety of 360 and PS3 games):
Animal Crossing: City Folk (game only)
Excitebots: Trick Racing (game only)
MadWorld
Wii Music

The sale ends on August 2, so you may need to hurry.