Customized listening: Pandora.com

The coolest website I've ever stumbled upon is free, customizable, sleek, and sweet. Pandora.com lets users (become a user by simply creating a login and password) create music stations that build themselves based on your preferences. If you choose a song, album, band, or solo performer the station will play songs with similar musical attributes, which you can then keep as part of the station or reject. You can create multiple stations, rate songs, and find out why songs were chosen. There are ads on the page, but no commercial interruptions to the music. Check it out!