Audacity is a free, easy-to-use and multilingual audio editor and recorder for Windows, Mac OS X, GNU/Linux and other operating systems. You can use Audacity to:
Record live audio.
Convert tapes and records into digital recordings or CDs.
Edit Ogg Vorbis, MP3, WAV or AIFF sound files.
Cut, copy, splice or mix sounds together.
Change the speed or pitch of a recording
For ubuntu karmic users
Open the command prompt and run the following commands
sudo add-apt-repository ppa:audacity-team/daily
sudo apt-get update
sudo apt-get install audacity
This is currently available for only karmic,lucid users