fdmf is portable perl/C software for finding pairs of music files in a
collection that are likely to contain the same music. It works on the
music itself, not on the filename, tags, or headers. It uses an audio
fingerprint, or perceptual hash to recognize the duplicate files. It is
currently under heavy development, so it might be buggy, broken, or
otherwise bad. But it works for me.

Author: Kurt Rosenfeld <kurt at w140 dot com>
WWW: http://www.w140.com/audio/