As a software developer, I open XML files all the time. I a heavy commercial XML editor. But nothing can compare to a small, thin and free XML editor like 'foxe'.
A great feature is has is the alignment of long XML strings to readable XML format (Shift-F8). It help lot of times when the XML file was generated by some tool and was not readable.
Comments
http://www.liquid-technologies.com/XmlStudio/Free-Xml-Editor.aspx
It has syntax highlighting, auto complete, creates an XSD from your XML, does XML Differencing, and many other features. Don't get put off by the 30 day trial, the XML Editor continues working after this as it is a genuine Free part of their product
-- Ziv