One of the challenges of podcasting is creating a polished work. Music in the intro or to segue can help you accomplish a more sophisticated podcast.
Some websites worth visiting and with great goals are:
http://www.soundsnap.com/ - Sound effects and loops.
As always, visit the licensing page of the website/artist to find out if and how you are allowed to use their work and what licensing you must make your production.
Have some websites you'd like to share? Please do!