The Music Genome Project has created Pandora, an on-line radio which’ll play the music you want to hear.
Enter the name of a musician or band, or the title of a song, and Pandora will present full-audio tracks of music which is similar not only in terms of tempo and rhythm, but things like syncopation, antiphony, synth or electronica influences, and more. It’s completely free (although a paid subscription version is available) and extremely interesting—if you find a new piece of music you like, you can purchase the song via iTunes or even get the whole album.