Well here's a trick I just did with PSP MixTreble that sounded pretty good to my ears - I checked this out and set it up in headphones so I think the results were even better.
I do a lot of remastering (non-pro just kind of hacking around for myself and friends) of tape to digital conversions. So the big thing there of course is broadband noise such as tape hiss.
The problem with all denoisers and hiss reduction is that it removes part of the good stuff. To prevent this you can obviously only turn on noise reduction when you hear noise that must be reduced - simple eh ?
If you have a host that allows VST automation, I use Sonar3, then insert a good denoiser across the track. PSP MixTreble has a hiss reduction section that is very good, what's equally as good is the VST version of the plugin is automatable.
I automate the attenuation parameter and turn it on only when it is necessary, in Sonar3 you can set automation control points in the same track as the audio so you can really fine tune it and make it very transparent.
That's the 2nd best way - of course the 1st best way like everybody else said is to track down the source of the problem and eliminate it before it gets committed to a recording...
Good luck denoising - a thankless and costly (timewise) job for sure...
ED: Oops forgot the link...look for MixTreble
http://www.pspaudioware.com/indexen.html?url=http://www.pspaudioware.com/plugins/mix.html;