Pandora is a very cool music website. You declare a few of your favorite musicians, and Pandora creates a custom radio station tailored to you. As you listen to the songs it has selected, you can “thumbs up” or “thumbs down”, further tailoring & tuning the music stream.
Now, Pandora is on the iPhone/iPod via the App Store… and it rocks! It works great over WiFi, and presumably 3G (Edge is hit & miss, says Sam).
You get a custom radio station wherever you are, with album art. You can bookmark songs & artists you like, and you can even buy songs via iTunes when you really find one you like.
If I can integrate it into my custom-car head unit, this will be the only radio I ever listen to again.