Pandora Radio is an internet-based website that plays music it thinks you'll love. You input your favourite track/album/artist and it comes back with other suggestions in the same vein. It's based on the Music Genome Project, allegedly the most comprehensive analysis of music ever undertaken. Once you put in your choice, Pandora scans its world of analyzed music to find songs with musical similarities (in terms of melody, harmony, rhythm, instrumentation, orchestration, arrangement, lyrics, singing and vocal harmony) to your choice.
I put in "Paul Simon" and so far I got two songs by Paul Simon, as well as Cat Stevens, Bob Dylan and Afro Celt Sound System.
Pandora streams music at 128 kbps. You need a broadband connection (DSL or Cable) of at least 150 kbps, and a browser like IE or Firefox. You also need a US Zip Code because their music licence requires listeners to be United States residents, but they're trying to make it available worldwide. Until then, you can have a go to see how it works by clicking on the link above.