[Read on, even if you are in the US].

I've been using this awesome service for over a year now and recommended it before, but unfortunately you need an invite to register an account, which are pretty hard to come by.
However, I do have some invites, which I wanna share here on Virb, so if you are interested, just comment or let me know otherwise.
Even if you are outside the currently supported countries (Sweden, Norway, Finland, UK, France, Spain), you can easily use a proxy server for signup and in the app itself, so don't worry. Just go here for instructions (ignore the LOST link, sorry for that).
You can also check out some apps available for Spotify, or tools like spotifyfm, listify, sharemyplaylists, or spotifylists.

About Spotify:
"Spotify offers you legal and free access to a huge library of music. All you need to do is create an account and download our streaming music player."