The Shazam app is pretty sweet for the iPhone, but I don't know if I'll shell out $4.99 for a premium version when the free one works fine.

 

...with a second, premium Shazam () application that will set you back $4.99. Shazam Encore, released today, includes added functionality like music recommendations, album reviews, hot and popular tagged tracks, music search, and the ability to dock your iPod/iPhone in your car and tag music playing on your car stereo.

http://mashable.com/2009/11/09/shazam-encore/