Depends on what kind of editing you want to do. If you're looking for basic
editing of an audio file, trimming and simple clean-up, then either Gold
Wave or Sound Forge are your best options. If you go the Sound Forge option
you don't have to buy it to get basic editing, but some features will be
disabled, and you'll probably want Sound Forge 7 for the highest level of
accessibility and ease of operation. (later versions lose some accessibility
and gain problems under later versions of Windows)
If you're looking for more of a DJ type environment then others will have to
advise you on that.