Has a good CD music extraction (ripping) utility, that uses the FreeDB CD database to look up and then store all the album and track details with your music files.
Supports several different "visualisers" - screen animations that move in time with the music.
Can be set to play music in the background after exiting (e.g. for background music during a MythGallery slideshow). Does not currently support music videos.
Read more in the MythTV Wiki entry for MythMusic