CLI Magic: Transform your audio files with SoX
Sound eXchange (SoX) is a command-line sound sample translator. This Swiss Army knife of sound tools can be used to convert file formats of your audio files, and to apply sound effects such as echo, fade-in/out, and chorus to jazz up your music with just a few keystrokes.
If you don't already have SoX installed on your system, the source is available on the project page. Fedora and Debian users can get it with yum and apt-get respectively.
SoX supports more than 20 formats; for a list of supported file formats, run sox -h. Converting files is as simple as sox file.mp3 new.ogg.