SoundHound for iPhone/iPad
SoundHound is an app that lets you see who the song your listening to is by and what it is called.
But you can do so much more. Like for instance you can sing lyrics to a song, hum a song, etc. and it will tell you who its by, what it is called, and even look up lyrics and Youtube videos for you.
Also, it will keep a history of searches you have done as well as post your favorites and whatnot to Twitter and Favebook if you wish.
Demo:SoundHound Free Song Search & Music Player
Developer: SoundHound, Inc.