Steam Music is now available with today's public beta client push and it basically turns your Steam client into a music organizer and music player. Sadly, it doesn't support WMA at this time so I can't access a lot of the music that I ripped into my hard drive from my CD collection. Which is a shame, because I definitely would just use Steam to play my music, but of course, not while I am playing my games. Still, I know a lot of players who love listening to additional music outside of the games that they play and this new implementation makes that a slightly easier process because the music option is in the Steam overlay.
It's a bit buggy but you can access your favorite songs directly from Steam!