Sitting on a balance ball at work is a great way to strengthen your core and improve your posture without any significant time commitment. But on the other hand, it looks ridiculous.
That, I assume, is why Gaiam made the Balance Ball Stool, which is just a stool with a partial balance ball attached to the top. Normally $129, you can get one from Amazon today for $103, and have it delivered to your office by the end of the week.