Part of the iLife package for Macintosh OSX, GarageBand is an easy-to-use software studio for music and voice. Record, edit, and save as MP3 files ready for podcast listeners.
ALSO! GarageBand can compose music for you in different genres such as light rock, jazz, blues, dance, house, hip-hop, and more. You can use a library of "loops" for parts and melodies, alter them, or compose your own. You can use any music thusly composed for anything you wish, royalty free, forever. This can fit the bill nicely for background or intro/outro music.
Apple's GarageBand Product Page
Apple also has online tutorial on using GarageBand to make Podcasts, too!