stability ball

Few days ago I accidently let my ball roll against the heater, the heat dissolved the side of the ball and created a hole.... So I went to Walmart and bought a 55cm stability ball today. Stottpilates has pretty good work out dvds. Their explaination about ball exercise are easy to understand.
Coincidently it matches with my yoga mat =) I just now have to be careful with this ball because it was $31 purchase -_-