WaveShop is a fast and lightweight audio editor, which despite its name supports lots of different audio file formats, including MP3, FLAC, OGG/Vorbis, and AAC/MP4. The program is bit-perfect, meaning uncompressed audio samples aren't altered unless they need to be; editing a portion of an audio file only affects that portion and the rest of the file remains untouched. Cut and pasted audio blocks won't modify their contents. This is especially useful for patching a finished master without corrupting its dither. Other features include unlimited undo, peak and RMS analysis, normalizing, fading, audio generation, and more.

Note that the author recommends running the 64-bit version (if you have 64-bit Windows) as it can load bigger files without running out of memory.

Alternatively, WaveShop Portable automatically switches between 32 & 64-bit and portablizes paths. X-WaveShop is also available.