We are regularly making some screencasts to demonstrate new functionality to our clients.
It would be good to have some nice, engaging background music playing throughout the show.
Are there any free tracks we can use legally?
AudioJungle.net - Best place to find this type of stuff, plus you can contact composers. The creators of the site also have VideoHive.com, which is a very powerful site for After Effects templates, which are great for presentations.
SoundClick has paid and free songs of high quality, just be sure to read the artist's description of what you can do with the music. However, there are frequently artists who give away music, or simply ask for attribution, which you can do at the end of the presentation/screencast.