XML Copy Editor is a fast validating XML editor.
Features:
* DTD/XML Schema/RELAX NG validation
* XSLT
* XPath
* Pretty-printing
* Syntax highlighting
* Folding
* Tag completion
* Tag locking
* Tag-free editing
* Spelling and style check
* Built-in support for XHTML, XSL, DocBook and TEI
WWW: http://xml-copy-editor.sourceforge.net/