Audacity should do it. It's freeware.
Note that if you intend to export as mp3 at some point, you will require a plugin. I think due to legal reasons, the plugin is not supplied with the software.
Also, people have reported that the app messes with the system sounds for mac. I personally have never experienced this, and it may have been fixed within the software. The developers were aware and I believe they provided a solution and explanation of the cause. Audacity is a great program though, and comes with a whole lot of features - more than a lot of shareware (and in my experience, less stable) alternatives offer.