I'm getting ready to get my stability ball and medicine ball too.
I have been casually shopping and have decided to get my stability ball from Fitness1st. I've been getting everything from them: barbell, dumbbells, barbell pad, step. Their prices are always a little lower than other places on the internet, (including fitness warehouse), and they don't carry everything, just quality stuff. Their service is great.
They sell the Gymnic Plus stability ball. The 55cm ball is $19.00. For people over 5'3" they recommend the 65cm ball, but I am 5'3" and will get the 55cm. (I know Cathe and Cedie are under 5'3" and use the 55cm ball in the workouts, but I haven't actually watched the workouts yet!) I think the website is Fitness1st.com
I haven't really shopped for the medicine ball yet, but my Fitness1st catalog does not show an 8 lb. ball. They do have a 6.7 lb. ball. I'm going to have to spend more time investigating this issue when I buy my next DVD. (For now, I've only got the pyramid DVD.)
-Nancy