The first software I tried is the one I'm currently using: Adobe Audition 3. I used the 2.0 version before the 3.0 came up.
I tried a lot of other softwares, but never found something more useful than Audition (in my case). I tried Pro Tools just for the sake of trying it, it's a very good program too, but I'm so used to Adobe Audition that I stayed with it. I didn't want to re-learn everything. Anyway, it seems that they are very similar.
Yeah, and Pro Tools is kinda wicked though. You need an M-Audio interface for the "M-Powered" version. And the others I'm not so sure...