The Hype Machine is on online music search tool that tracks a variety of MP3 blogs. If a post contains MP3 links, it adds those links to its database and displays them on the front page. Some of the frequently accessed tracks are cached by the Hype Machine server to reduce load on the bloggers' servers and protect their bandwidth. Those tracks are not available for download, but you can preview them via the play buttons that are next to each track. The blog that posted a particular track is identified under every track by name so you can read more about why they posted it.