Have you ever heard a really great song or tune somewhere online without knowing its title or author? It's a unpleasant feeling. These days, there exist many apps that you can have listen a song in the background that will recognize it for you. I've been using Shazam for a few weeks now and I'm very happy.
Shazam recognizes songs after a few seconds of listening. You can buy the songs from the app. Shazam runs as a browser add-on. It's free to use.