DeNoise

I would rate this product as excellent if it weren't for the somewhat quirky user interface. Aside from that, this is an incredibly useful product! It removes noise without any audible artifacts. Being the owner of a mastering studio, this application has come in handy many times over, especially when clients send in mixes that obviously have noticeable background noise.
Also, being a recording musician, this app is especially useful on tracks that have been recorded using a microphone, and where unwanted background noise (e.g. computer fans) has also been captured on the track.
I give it a hearty thumbs up!