I'm looking for something challenging that can be used with a 55 or 65 cm ball. Either strength training with weights, or pilates type exercises.

Any recommendations?

I would check e-bay. I started Turbo Jam a few months ago, and have gotten bored with the starter set. I got a set of add on dvds to the Turbo Jam collection, and there was either two or three exercise ball dvds in it. They are great! They are also sold individually, so you don't have buy the whole kit and caboodle if you don't want to.

Thank you!!!

I got a dvd off of ebay called 10 minute solution fitness ball workouts. It is 5 10 minute workouts that you can do one at a time or seperately. I did them all at once and couldn't move to 2 days! It's a kick your butt workout! But I am a beginner so not sure if you are advanced. HTH! Hugs, Chrissy