I always encourage people to use their own music creations in the videos they produce, but I recognize that that is not always possible or practical. My next recommendation then is to use Creative Commons licensed music (here are seven good sources). This morning through Pitchanan Gaysornmas I learned about another good place to search for and find Creative Commons music, the Vimeo Music Store.
The Vimeo Music Store offers more than 45,000 music tracks. Not all of the tracks are free or Creative Commons licensed, but roughly one-third or more of them are. In the Vimeo Music Store you can search for music by genre, license type, price, and length.
Applications for Education
The next time your students are developing multimedia projects for your class, have them take a look through the Vimeo Music Store to see if they can find a tune to enhance the message of their productions.