Math Podcast's for 6th Graders?

I have recently created a podcast in a graduate class. It was fun to create and I find that it can be very informative if done correctly.  However, it was very time consuming. So until I build up a collection of my own podcasts, I am wondering if anyone knows of any good podcasts that are already created form implementation? Also, what ways have you found as the best way to implement a podcast effectively?