Audacity -- http://audacity.sourceforge.net/

Audacity is a free, open-source audio program with which you can record, edit, and play sounds, import and export WAV, AIFF, Ogg Vorbis, and MP3 files. It also features level meters, multi-file export, and low-latency multi-track recording. This program is available for Linux, MacOS-X, and Windows.