The best of the five programs that I have that are capable of that sort of thing is Corel Photopaint, which comes with Corel Draw, might add there are also a bunch of other things that come with Corel Draw.
You should scan it in a lossless format (BMP if that's the only option) rather than JPEG since with JPEG you tend to lose a bit of the quality and is therefore bad for editing.
Great question! Although what exactly are you trying to do?? Most large software packages such as corel and adobe are expensive. I think most would agree that the best free peice of editing software is GIMP. Although there is a very good hosted solution at http://pixlr.com/editor/ which i quite like