I'll second the opinion on noise ninja, however I have found that significant noise in an image has been impossible to fix. For example, over ISO 2500 on a D700 I just won't do it anymore, which is fine for me.
I still use a D70s which has horrible noise, probably worse than anything you'll get from a D700. That said, I have run into cases where Noise Ninja seems to break down, but you have to train Noise Ninja to look at the image differently by selecting your noise zones very carefully. Noise Ninja's auto find noise algorithm can be fooled quite easily. If you choose the targets with scrutiny, it'll perform much better. In some cases I use the removal by color instead of luminance option and it works much better.
I tried Topaz Denoise recently. Not too thrilled with it. Seems content specific. On some images it works well, on others it completely craps out or blurs too much regardless of settings. I met the developer of the software at a tradeshow where he was giving demos, and boy what a cockey jerk. He was bragging how much better denoise was and how it uses an algorithm not based on spectral analysis and wavelets like Ninja and other competitors as if denoise was the undisputed king or something. I wanted to see for myself how the software worked, so I offered an image off my flashcard from a photo shoot the previous evening to test. He did everything possible to avoid demonstrating his software from ducking questions, to changing the subject, to eventually flat out ignoring me. I just wanted to see how his software works, didn't care if it was on the floor or after hours where nobody else would see. But he still flat out refused to demonstrate the software on anything than his canned demos which consisted of two images - a pizza and a coffin from a museum shot. When I asked to see other settings applied to his canned demo images, he still refused to make adjustments. yeah...I'll buy his stuff. I went to competitors in other booths and all of them accommodated me without issue.