Izotope RX.

This software does miracles. It has a fairly large learning curve for the more advanced features, but it's a very powerful software suite, especially for the price.

I use it mostly for getting rid of my noise floor in recordings, but I have also used it for removing audience coughing in live music performances, clipping noise, etc... Works as RTAS, AU, VST, Audio Suite, and Stand Alone. Freaking awesome!