I had the chance to spend some time with Izotope's RX audio restoration software at MusikMesse in Frankfurt and was very impressed with how advanced audio restoration software has become.
RX iincludes the usual noise removal tools such as a hum removal and declicker, but even those show impressive flexilibity, such as a manual declicker mode. When combined with the unique spectrogram display, you can easily find intermittent noises and completely remove them. The software can actual "rebuild" the audio - you would never know it was there! This amazing (almost magical?) ability to rebuild and repair audio shines through in the declipper, which can remove analogue and digital overload distortion, and in the spectral repair module. The spectral repair fills in gaps in audio and can even account for changes in pitch, vibrato and harmonics.
If you are looking for an automated, easy to use, "press one button and go" type of audio restoration software, then RX isn't your best choice. However, if you have noise you need to remove, and want the best results possible, RX is an amazing tool that I can highly recommend.