Soon! Wii Fit Plus
Next month there will be a new addition of Wii Fit, name Wii Fit Plus.
Wii Fit™ Plus, which builds upon the original Wii Fit™ software, works directly with your Wii™ console to bring you a fun and exciting way to experience fitness. Get fit with over 60 activities and exercises, including over 20 new strength training, aerobics, yoga, and activities—or create a customized fitness routine for your needs, new to Wii Fit Plus.
(source wii.com)

The standard version Wii Fit includes the balance board and the Wii Fit software and is a great alternative to excercise at home.