Shazam is definetly the most useful app I have found so far, and it is free. You just click on it, hit “Tag Now” and hold it up to whatever is playing music and a few second later it will tell you the song, artist, and album. I personally use it for album identification for all my old mp3s, that don’t have a lot of good meta information. The only thing I wish it did have was the track number of the song. Shazam is not flawless, but then I was playing a recording of No Doubt covering “End of the World” by REM at the MTV 1999 New Years Eve party.