Though the app is free, Rdio
operates on a subscription-based model: $10 a month. Still, forking over the dough gives you unlimited access to a trove of 10 million songs, which you can listen to on your Android device over Wi-Fi or 3G. You can also create playlists, sync music to your device for offline listening, follow friends and persons of interest in the music biz, read user reviews, and get recommendations based on your listening history. Even with the arrival of newer competitors—hello, Spotify!—Rdio remains the best music discovery app out there.