You can buy applications for the iPhone that do some incredibly useful stuff.
One of the most popular (and free) applications available for the iPhone is Shazam. Open this app and let it listen in on whatever music you are hearing and it will sample enough of the music to analyze via the internet and then tell you the who and what about the music within a minute. It stumbles when ambient noise is too high, but I've had success while watching TV commercials and in a store.
I have lost count of the number of times I could have used a tool like this.