When creating a podcast or a video one of the most difficult things is to find music for the background that is free, especially if you will be showing your project off on your web page or outside of the classroom.
One of the best ways to avoid this is to create your own music. This can be done fairly easily with Garage Band or you can record your school choir, orchestra or jazz band.
If you can't do this, or choose not to here are some sites that offer truly free audio for school use.
Sound Snap Web 2.0 looking site. Lots of sounds that are free to use remix and publish. You can download 5 sounds a month with a free account. You must have a log in.
Free Loops This site has over 8000 loops of music that you can use for free. There are sound effects and also links to other information. Can be searched by Creative Commons license.