The most popular for PC based DAW's is CoolEdit, which went belly-up and was purchased by Adobe. It is now called Adobe Audition. They are working on a Mac version called Production Studio. For Mac's, Pro-Tools. Go with Pro-Tools LE (Lite) it is more affordable than the other versions of Pro-Tools, the software is free but you must purchase the M-Box 2 mixer to use the app. Pro-Tools is now on the PC platform as well. As mentioned by AvgListener, there is Pro Logic which is strictly Mac only because it's made by Apple. I haven't used it, but I've heard that it is a little harder to learn but is a sweet app.
Punjistx