How do I play music on Ubuntu without having to launch the X Window system?
There are many command line programs for audio playing like mp3blaster, MOC, Cmus, Cplay.
MOC (Which stands for music on console) is one of the most prominent and it's easy to use. It has convenient ncurses interface (GUI-like command line interface) and supports MP3, OGG, WAV and other most popular audio formats.
After starting MOC with
command, you can select file which should be played. For list of command press 'h' key. Most useful are 'a' and 'A' key commands that add file or directory recursively to the playlist and 'q' command which closes interface but leaving server running so music still plays. To get to the interface simply start MOC using mocp command again.
Although simple, MOC is very powerful so it can be configured in detail and enhanced with plugins.