Is there really good distortion correction software?

Hugin software allows for highly precise control of horizontal and vertical lines, and it can detect and correct for lens distortion. Not only can it produce a rectilinear image from ultrawideangle lenses, it can do all sorts of mapping: a cylindrical projection might suit your subject better than a rectilinear projection.

It is also free!

However, it is rather difficult to use. Don’t expect it to operate automatically, and don’t expect to get usable results quickly. RTM.

--
http://therefractedlight.blogspot.com