Windows

• Audacity - Audacity is a free audio editor. You can record sounds, play sounds, import and export WAV, AIFF, Ogg Vorbis, and MP3 files, and more.
• Arial Audio Converter - Convert audio formats between MP3, WMA, OGG, MP2, WAV( PCM,DSP,GSM,ADPCM ),G721, G723,G726, VOX, ALAW, ULAW with different settings. Free trial.
• Sound Forge 7.0 - A full featured commercial sound editing application. Free trial.

Macintosh

• Audacity - Audacity is a free audio editor. You can record sounds, play sounds, import and export WAV, AIFF, Ogg Vorbis, and MP3 files, and more.
• BIAS - Peak - A full featured commercial audio editor for OS X