I've always used CoolEdit for that purpose. Very cool program, and very easy to use. It isn't free though.

Note : I've only just found out now that Syntrillium (the company that made CoolEdit) has been bought by Adobe. It seems that the CoolEdit software bundle still exists, but that it's now called Adobe Audition 1.5.
http://www.adobe.com/special/products/audition/syntrillium.html