For cleaning constant background noise (aircon/traffic etc) Soundsoap from Bias works very well.
I use Peak for most tweaking getting rid of pops, soundsoap can work within peak as well.
Digidesign makes a plugin called "DINR" (it's broadband noise reduction) if you have access to a pro tools system... that's what I usually use. By the way, I would suggest doing a search in the audio section becuase I remember seeing a post in there that had a ton of ideas for this sort of clean up, too.