Audacity

Audacity is a free, easy-to-use audio editor and recorder for Windows, Mac OS X, GNU/Linux and other operating systems. Audacity can record and play sounds and import and export WAV, AIFF, MP3, and OGG files. Edit your sounds using cut, copy, and paste features (with unlimited undo functionality), mix tracks, or apply effects to your recordings. The program also has a built-in amplitude-envelope editor, a customizable spectrogram mode, and a frequency-analysis window for audio-analysis applications. Built-in effects include bass boost, noise removal, and the program also supports VST plug-in effects.

Features:

• Record live audio.
• Convert tapes and records into digital recordings or CDs.
• Edit Ogg Vorbis, MP3, WAV, FLAC or AIFF sound files.
• Cut, copy, splice or mix sounds together.
• Change the speed or pitch of a recording.
• Add new effects with LADSPA plug-ins. 
• And more!

Homepage:

http://audacity.sourceforge.net/ 

Download:

http://audacity.sourceforge.net/download/