WaveShop is a free, open-source audio editor for Windows XP/Vista/7.
Unlike many similar apps, WaveShop is bit-perfect, i.e. samples aren't altered unless they need to be. If you edit a portion of an audio file with WaveShop, only that portion is affected; the rest of the file is untouched. This is useful for patching finished masters. Waveshop's features include cut/paste, peak and RMS analysis, normalizing, fading, audio generation, and more.