At the bottom end of the scale you might want to try Voxengo's Redunoise ($100), and at the top there is [Sonnox Restore] [$1900]5. Personally I would stick with [Nuendo] or purchase Wavelab 7 when it is released later this year, as it will have the Sonnox Restore tools built in for about $700.
There are further excellent comments about noise removal software within the post "How to clean a digitally distorted recording."
+1 for iZotope, excellent value for money, works as a plug-in or stand alone. See my review here
Hope that helps