SmillaEnlarger
SmillaEnlarger is an open-source and portable application designed to help you intensively massage an image enlargement to keep it from looking jagged and filled with artifacts. You can select the level of zoom using the zoom slider and the location of the zoom via the selection box. Once you have the selection you're after, you can begin tinkering with the sharpness, flatness, dithering, noise levels, and more. The preview function is quite speedy so don't hesitate to preview often to check how the various settings effect the outcome of your image.
