For those of you wanting a fairly good audio editor for free, that works on either Mac or Windows (and even Linux, for the propellerheads among you), I suggest checking out Audacity. We will actually do some of our classroom editing on Audacity, as it comes with a built-in noise reduction process.
Audacity is open source. It supports VST plugins and many file types. You do have to check the web site for updates on your own.