Mediamonkey

A Windows-based media file tagger & organizer, complete with a built-in media player.

The media player can use most Winamp's input, output, DSP, and visualization plugins.

Unlike many media players, the user interface is themed as a media library.

The free version, is, well, free. The Gold version (which adds, among others, automatic/periodic scan of "watched folders".)

http://www.mediamonkey.com/