MuseX is a multimedia player for Garry's Mod. It has the ability to play a multitude of audio formats, including, but not limited to MP3, Wave, Ogg Vorbis, Windows Media Audio, and Midi. MuseX allows you to browse and play music from any directory, on any drive on your computer, with it's fully functional media browser.

FP Thread: http://forums.facepunchstudios.com/showthread.php?p=8803190