I remember when I first heard about fitballs and stability balls I thought they looked both hilarious and fun, and so it was great that they had such sound principles behind them. Today you can find stability balls everywhere, along with every kind of workout you can imagine. They're great for strengthening your core, improving balance, and toning pretty much everything, but in order to get the most out of your efforts you should make sure you're doing all the moves and using everything correctly -- even down to having the right sized ball.

eDiets has a handy chart for figuring out what size stability ball will work best for you based on your height (or just sit on it and if your thighs are parallel to the floor it's perfect), plus they've listed some good basic stability ball moves complete with animated pictures.

So if you're not already, get on the ball! And have fun (try not to roll off!)