Ian,
The two leading NR tools are those included with Sound Forge and iZotope Rx Pro. Far more important than the tool is the skill of the person using it. This comes with practice. NR has the potential to seriously damage the sample by 1) introducing digital artifacts, 2) attenuating or destroying upper harmonics and inharmonic content, 3) attenuating fundamentals, and 4) dulling attack transients.
Tips for NR: 1) remove only as much noise as necessary to have a usable sample, 2) use multiple passes with small cuts, 3) experiment with FFT size to find the value that produces the best results for the rank, 4) generally,set the attack parameter to the fastest setting, 5) do only one note at a time, 6) alternate source for capturing the noiseprint between the start and end of the sample, 6) after each pass, A/B the processed sample with the original unprocessed sample and make a judgement when to stop, 7) single frequency artifacts might be amenable to 1/3 octave notch filtering, 8 ) broad spectrum artifacts like "phasing" or "under water" effects cannot be fixed.
If this sounds like a heck of a lot of tedious work, that's because it is!
Joe Hardy
Paramount Organ Works