Shawn sent out a cool link to Pandora today. I've been playing with it for a bit and it's pretty darn cool. What is Pandora? It's a very simple streaming music service that generates streaming content dynamically based on your music preferences. You simply tell it about a song or band you like and it delivers music that has many of the same characteristics of what you like. So far, it's proven to be pretty accurate. I've already found a couple of new bands (The Exies is my current new favorite). They've also partnered with Amazon so if you decide you'd like to buy a CD, simply click.
To me, this type of service is a lot more valuable than iTunes because it allows me to learn about new music I might like.
Oh, Pandora is also (a) free and (b) based totally on Flash so there's no install. Try it out!