Most of the dedicated video editor programs have a range of filters to help correct problems. It really depends on what you need to do and how much. For the money, Ulead VideoStudio 10+ is about as good as it gets, but Adobe Premier is also top quality for the average Joe. Either one will have some learning curve to work through.

Personally, I find that such filters tend to introduce some objectionable qualities as often as they remove them, so I usually just go with the best quality conversion I can get and then just adjust my monitor as needed. The one thing you can't do is ADD clarity or resolution.