Get Shazam. Not always useful, and maybe not a 'gotta have' but for the situations in which you'd use it, its awesome.

Ever been out to a bar, restaurant, mall, or even just listening to a radio, and a song comes on that youve heard a milliion times, or maybe just sounds familiar? Hit up Shazam, and it will use the phone's speaker to listen to the song, then tell you what it is.