Camtasia is screen capture software, not really a full blown editing suite. I own a license to camtasia and I use it to make tutorials, and training videos at work.
Really, you need to look at Final Cut, Premiere, video toaster, or the like to get real professional editing features.
To be honest, iMovie HD for Mac OS X is pretty powerful for what it is. I think there is also an Adobe Premiere light or something too.