oXygen XML Editor and XSLT Debugger
Oxygen is a multi-platform XML Editor, XSLT/XQuery Debugger and Profiler with full Unicode support. It offers a powerful code insight that can follow a DTD, Relax NG or an XML Schema or even can learn the structure from a partial edited document. XML and XSL documents can be easily associated... Oxygen validates XML, XSL, XQUERY, FO, XSD, RNG, RNC,NRL, DTD, Schematron, WSDL and CSS content, reporting errors with description and line number information and marking them in the document when validate as you type is enabled.
http://www.oxygenxml.com/InstData/Windows/NoVM/oxygen.exe - 16Mb - Download - Screenshot