Adobie Audition is the Photoshoph of sound. I can not tell you all the features but a few that I use a lot are: removing background noise, Speeding up and slowing down music with out changing pitch, the editor is an easy cut and paste, and the mulit tracking is amazing, it has a many built in plugins.
It used to be called Cool Edit pro before adobe bought it and I kind ok liked Col Edit better but I was unsed to it.
http://www.adobe.com/products/audition/