Note: Updating from versions prior to 0.3 requires reactivating!
Media Downloader plugin lists MP3 files from a folder through the [mediadownloader] shortcode. It reads MP3 information directly from the files. It also can try to get rid of stupid content blockers (mainly corporatives), changing all links to .MP3 files into some download URL without the string “MP3”.
This plugin is available for download for your site.