philipglass.com
Kenny commented that he enjoyed Philip Glass's music from the Fog of War. He has been one of my favorite composers (Glass, not Kenny)--if a bit smooth around the edges in his older age. It may not be your cup of tea, but even if you don't enjoy his music, I thought you might be impressed by his web site. When you get there, launch "The Glass Engine" (the impressive part). You can hear any piece he's recorded through 2002. Every track, from every recording. Sort chronologically, or by tempo, density, level of joy, sadness (really)...

It is the greatest musician's web site that I know for providing music. If every artist did exactly this, I'd never leave my computer. Oh wait, I never do. What are your favorite, most impressive web sites we should know about?