Incompetech has a large selection of original music tracks that are free to use for any purpose, including commercial use - if attribution is given in the video. If you don’t want to include attribution then the composer wants $. He’ll also do custom original compositions, for $ of course.
Several of the tracks are very popular for use on YouTube videos.
The same site also has some very useful graph paper generators. Input your parameters and it makes a PDF to download and print as much as you want.