I've got a TON of music on my external harddrive, and I haven't felt like putting all of that music on my new computer or phone. It just takes up too much space. So I decided I'd set up a cloud radio player for it with an iPhone app to listen. So, I turned one of my Pi's into a lamp server with mysql and php and made it public facing. I then wrote a small PHP script that filled the database with 3 columns: the name of the song, the artist, and the path on the harddrive to the audio file. From there I just made a simple iOS app that queries my db and fills in a list of the songs, then streams from my Pi. It's pretty sweet right now, it shuffles the playback and retains the filtering options through the shuffling (so if I wanna' play Jimi Hendrix music, it'll shuffle Jimi). It plays in the background. The next step will be querying some online db of album artwork to put up/show in the background. Here's a screenshot of my app: http://imgur.com/dQzHYSe

I'm thinking of open sourcing the app and writing a really detailed tutorial of how I did it all on Github. Anybody want something like this?