Free Audio Editor
Here's another tool intended to satisfy all your everyday audio processing needs - those which you are reluctant to pay for, but for some reason wouldn't mind attending from a feature-rich centralised interface. This audio editor is capable of dealing with files in most common formats (although none of the lossless ones is supported) and even record audio from chosen sources. Besides the basic editing tools (cut, copy, trim, and so on), it also offers a variety of effects and advanced tools like fade in/out, normalisation, compressing, enveloping, speed/pitch changer, a number of filters, chorus, flanger, reverb, and a bunch extra. All these tools are easily accessible from the top panel of the main window and also a tree-like interface on the left, the handiness of the latter being somewhat arguable.
The program does, however, retain the major disadvantage of all 'sub-professional' free tools, namely its black-box principle of operation: most of the time, you just load a recording, select a portion of it, choose an effect, and then see your sound processed by means of some unfathomable magic. There is often no explanation given as to what parameters of the recording are affected by this or that effect, and you cannot affect their operation, either. There is, for example, a noise removal tool offered, which could make a big difference and make this editor really stand out among its competitors - if not for the way it works: I open a file, select a noisy portion of it, and press 'Noise Reduction' - and all I see is a progress bar appearing for a split second, and then the portion I selected gets filled with silence. No threshold customisation, no base frequency, no noise shape detection, nothing.
And even when you do actually get to fine-tune some parameters, you still have to go a long way before you get the intended result, as the choice of those parameters is often not only scarce, but also quite dubious. For instance, the peak level of Normalisation is supposed to be specified in percent of the maximum (0db) level - so if you're processing your recording for radio playback (and thus need -0.3db as your peak level) you're practically left to guess how much you are supposed to subtract from 100% to get that value. How much is 50% between 0 and -inf anyway?
In short, feel free to use this program for cropping your MP3s and applying some fancy effects to familiar sounds for a laugh or two - it will do nicely; but don't expect anything beyond that.