Audacity

This is one of those on top 100 downloaded at sourceforge.org. I'ts a good audio program. With Audacity, you can edit wav, mp3, and ogg's. There are many tools and effects that you can use to enhance or change your audio. You can have an unlimited amount of tracks. Save and export in various formats like wav, aiff, ogg, and mp3(with lame [that's what it's called] mp3 DLL). It's really pretty easy to use and there isn't any useless buttons. I have used this type of program before for repairing audio, making music and making the sound tracks for a movie project.

Get Audacity here.