According to this article on MTV.com there will be a Ninja game - "Ninja Reflex" released on the Wii in March.  This game might be interesting and possibly a good workout.  The article states:

"The upcoming game, set for release in March, consists of six mini-games: nunchuck swinging, katana sword-fighting, shuriken-throwing, firefly-catching, fish-catching (by "hand") and ensnaring flies with chopsticks. Each involve just the Wii's remote controller (not, ironically, the secondary nunchuck) and can be played in multiplayer."