Noise reduction and audio restoration are a signature skill of Bias Inc. The company's SoundSoap and SoundSoap Pro have been music industry staples for a long time. SoundSoap is even included in Roxio Creator 2011 Pro. But those products are expensive. Enter SoundSaver ($50, 14-day free trial), which not only implements noise reduction, but records, splits and saves multi-song recordings as well.
SoundSaver is simple, attractive, and easy to use, but there are other simple and effective recording apps available. The reason to buy this program is the quality of the noise reduction, which is nothing short of superb.
The program previews all noise reduction during playback so you can adjust the various parameters such as Remove Clicks/Crackle, Remove Noise (mostly hiss), and Enhance and hear them in action before committing to them. Enhance is an SRS Wow-like adjustment that increases the bass and overall dynamic range, which can offset some of the frequency-loss induced by noise reduction.
I do have a few gripes. SoundSaver didn't automatically detect my default audio input and output. I pressed play a few times with no response before I realised what was wrong and set them myself in the preferences dialog. I had to do this every time I loaded a file. My other quibble was that when saving the entire track without "defining tracks" (that is, splitting the file in to multiple songs), I was given no chance to rename the exported file. This could cause an accidental overwrite of imported, non-processed material if you're not careful.
Taken in the big picture, those are piddling complaints that the company assures me will be addressed in short order. In truth, SoundSaver is a steal. You get top-flight noise reduction at a fraction of what you'd normally pay for it and a handy recording app in the mix. A one-stop, home audio restoration station par excellence.