We've been developing some Winamp plugins here at Intelligent Sound project. This is an academic project - you can read more about us at our homepage:
We believe our plugins are useful enough to be released already.
The features that might be interesting to you at the moment are real-time genre extraction and searching for similar music. Please note that we don't perform any keyword-based search - our search technology compares sound itself, using the state-of-the art algorithms developed in our project.
When you play songs in Winamp, our plugins gather some information about the sound and upload it to our database. The information consists of artist, title and other metadata, which can be read from ID3 tags of your songs. We also calculate some coefficients concerning the sound itself. You can read more about this in our publications.
If you are interested, send yourself an invitation to the MiRocket system. The number of invitations is very limited, as we don't want to overload our servers. After you receive the invitation and you register, you will be able to download the plugins.