Any good gym ball exercises for stomach, bum and thighs please?

Just bought a gym ball and love it but im bored with the exercise sheet that i got with it. Ive done the squats, sit ups etc now I need something different. Plus if anyone has any tips on mastering balance on it that would be great! Still practicing
Answers:
If you want a sexy core, then grab a weight and rest your lower back on the ball as you support your body up with your legs. With your arms extended, move the weight from one side using your sides and bring it back to the other side.

For your bum, try putting your feet on the ball and get into a push up position. Raise your bum in the air and then lower it slowly. It works if you do it right. Some people say it works their abs more, LOL.
Abstaining from drinking alcohol would certainly help with balancing on a gymball (though entertaining) or www.gymball.com/exercise.html