Xtreme Media Player is a very simple, free and open source audio player, written in Java, that you can use to listen to your audio files.
It supports mpeg audio (mp3), ogg vorbis, flac, speex, wav, aiff (aifc, aif) and au (snd). You can also import playlists in xspf, m3u and pls format.
Xtreme Media Player recognizes the IDv3 audio file tags and displays them in the playlist, so you can easily recognize your songs in the player.
Furthermore, Xtreme Media Player includes a number of options to further customize this excellent player.