Are you still buying CDs or single MP3s from retailers? To save a few bucks, sign up for an unlimited music streaming service instead. Spotify offers a vast database of tracks -- more than 15 million in total -- and lets you play these back on your mobile device for just $9.99 a month (for Premium membership). Using the app, you can listen to your tunes offline, share music with friends, star your favorite tracks and sync your best playlists. Deep social integration with Facebook and Last.fm adds inestimable fun to your music consumption.