Here are some things I'm supposed to do with the stability ball: chest fly, rows (tummy down on ball), lateral raises, bicep curls, elbow extensions, hamstring curls, hip extensions, abdominal crunches (on the ball), abdominal crunches (obliques against a wall)...

They aren't terribly expensive...maybe around $40 - $60. If you are going to use it consistently it's better to get it at a fitness store rather than the ones you can find at WalFart. Make sure it is an anti-burst one.

I like the ball....there's a lot you can do with it.