I've written a few Raspberry Pi tutorials, but when it comes to music, I wanted a media server that could play my music library anywhere I was at (with an internet connection, of course). The RuneAudio Raspberry Pi works well for music when I am sitting by the Pi and can jack in with my headphones or speakers, but if I'm at work, the Rune Pi can't pipe the tunes to me at my desk from home.
For this, I've chosen to run Subsonic, a free media server that can handle both audio and video files, and stream them to any web browser on the net, or a dedicated phone app.
While I could play my music on my phone or from the laptop, it's pretty cool to have your own server sitting at your house that you can play your music from anywhere you are, and accomplishes my goal of having a single source for media. I don't have to move media files to every device I have anymore. I just load the files to the Raspberry Pi and I'm done.