De-coder.com

MPXPLAY
DOS player that supports mp2, mp3, aac, ac3, dts, ape, mpc, ogg, wav, and cd.
www.geocities.com/

Winamp
The leading high fidelity music player for Windows 95/98/NT that plays MP3s, MP2s, WAVs, VOCs and MIDIs.
www.winamp.com/

Apple - iTunes
Free MP3/AAC player/organizer for Mac and Windows that tags, rips, burns and converts audio files and integrates with the iPod portable music player and iTunes music store.
www.apple.com/

MPEG4IP: open source MPEG4 package
MPEG-4 AAC audio encoder, MP3 encoder, MPEG-4 video encoders, MP4 file creator and hinter, IETF standards-based streaming server, MPEG-4 player. Mostly Linux-based.
mpeg4ip.sourceforge.net/

Quintessential Player
Multiple audio format player with advanced visual effects and a plug-in architecture.
www.quinnware.com/

Free Lossless Audio Coder
FLAC is an open source lossless audio codec, supports streaming, seeking and archival.
flac.sourceforge.net/

NGWave Audio Editor
Sound editing application, record, process, and save sound or music files. Product specifications, screenshots, tutorial, FAQs, and downloads.
www.ngwave.com/

XMMS
X Multimedia System, an open-source MP3 player for Linux. Contains mostly the same features as Winamp and supports skins.
www.xmms.org/

True Audio
Open lossless audio codec developed with the main requirements of reasonable compression level and high operation speed.
www.true-audio.com/

Steve Ekblad's Free Audio Software and Online Audio Tools
A variety of acoustics related software tools geared toward the do-it-yourself experimenter.
www.audiogrid.com/