We need to get out of the box of using the same default music available in iMovie and FCPX.
Here are some sites providing audio downloads. Licensing varies, so be very aware of what you download and whether you credit the creators, pay, or get other CC licensing.
Huge site with tons of great stuff. Education licenses are free, but you do need to pay $1 a year if you are submitting your film to a festival:
Lots of great music available. Get a free CC license by giving credit to the artist. Non-commercial use only for free licenses.
Great music. Limited downloads. No license.
Tons of live music from bands along with other public domain tracks.
Post from Game Development Site with links
Sound Effects/Star Wars/Star Trek etc.
More cool electronica with no copyrights: Student favorite!
Tons of Creative Commons licensed music: Student favorite!