While finding just the right piece of music is a blast, the music industry is a draconian world. Seriously, the licenses related to music are so complex that getting the rights to use a song can take months and might require dozens of people.
Fortunately, some companies realized that this was crazy and needed to be straightened out. Below are the two companies that we use to legally license music for all of our video projects. They each have their pros and cons but both are light years ahead of doing it ourselves or stealing music.