I didn't know where to put this thread, I apologize if it's the wrong subforum.
Songza is a free iOS, Android, Kindle and web app and it's awesome. It's basically an app that plays playlists for you depending on the time, your mood, where you are, what you're doing etc.
There are many features like browsing playlists by genres etc. You can also turn on HQ sound, choose which earphones you have and it optimizes the sound for them. You can thumbs up/down a song so the app knows what you (dis)like.
Here are some screenshots, check out the app.