Windows only: If you're delving into XML programming for the first time, or want to tweak a few software files, Microsoft's XML Notepad 2007 may be the no-nonsense editor you're looking for.

New features of oXygen 2.0 include the ability to view and edit a XML document as a graphical tree; spell checking; enhanced support for XML Catalogues; the ability to configure external tools to ...

MS XML Notepad 2007 <BR><BR>edit: just to clarify, this is an xml file editor that has a tree view pane on the left. You can right click and expand the whole tree, or leave it collapsed.