Pandora is a neat free little thing on the internets that reccomends music to you based on what artist or song you reccomend to it. But unlike other music services, it reccomends music to you based on what their staff "music analyzers" say about songs.
For instance, I entered a station for the Violent Femmes. It first reccomended their song "Nightmares" because it has "acoustic rock instrumentation, grunge recording qualities, subtle use of vocal harmony and major key tonality."
Who knows what "grunge recording qualities" and "major key tonality" might be, but hey, it sounds good. Behind all of the fun technical music theory stuff, there's some good music to be reccomended.