I am updating this from over on our Spoiltchild blog.
A good podcast logo is hard to find. Here is one we designed and it is free for you to use on your own website.
In the attached file selection of file you can find various file types and sizes for anyone to use anywhere. It includes transparent .png files to place on different backgrounds.
I do require a link back if you use the icon from anywhere on your website.
Podcast icon from Toddle <a href="http://www.toddle.com/">Email Newsletter Templates</a>
Let us know if you use it so we can see it in action.
You can find other free images for your email or website here.