Linux MP3 Players

XMMS
XMMS is a multi-format audio player capable of playing WAV, MOD, MID and MP3 files. It provides features such as playlist function, CDDB, CD Index,  Wheelmouse change volume, visualization plugins, compatible with Winamp's .wsz skin files and more.  XMMS is not a freeware, it's GPL (open source)

mpg123
From the developer: mpg123 is a real time MPEG Audio Player for Layer 1,2 and Layer3. (MPEG 2.0 with Layer1/2 not heavily tested). Tested with Linux, FreeBSD, SunOS4.1.3, Solaris 2.5, HPUX 9.x and SGI Irix. Plays Layer 3 in stereo on an AMD-486-120Mhz or (of course) a faster machine. (Just for info: mpg123 plays an average 128bps stream, with about 66% in full quality on my AMD 486-133MHz machine) Note: this player is only for non commercial use.