This has my vote probably for one of the cooler free applications on the App Store, called Shazam. Check out the story here.
My experience with it showed it to be satisfactorily accurate — it knew a lot of less than commercial songs. Shazam says it has a database of about five million songs from which to work with.
While an offering it does in the UK costs money per use, and its port for AT&T customers seems to also charge per ID as well, the fact that this is free is pretty nice.
Shazam tag screen
