LiveXMLEdit is a tool for inline editing of XML files. It renders the uploaded XML file and lets you create and delete nodes and attributes, as well as update their values by clicking on them directly. If you don't see a dedicated save (Submit) button, use the ENTER key to save. Once you are done editing the file, you can generate the new version and save it.
LiveXmlEdit is optimized for Firefox, Google Chrome and Safari. It will work just as well in Internet Explorer 6/7/8 but won't look as pretty.
A blog post about it: (http://www.subchild.com/2009/10/16/live-xml-editor/)
Update on latest version: (http://www.subchild.com/2010/08/26/live-xml-editor-version-1-5/)
LIVE DEMO: (http://www.subchild.com/liveXmlEdit/)