Here are some of XML editors and their reviews:
The W3C's test editor/browser has been updated to full version 3.1. New features include expanded support for MathML and XHTML, line numbering in source files, link creation from the keyboard etc.
-EditiX Lite - Free XML Editor
EditiX Lite is a free and powerful and easy to use XML editor, Visual Schema Editor and XSLT debugger for Windows, Linux and Mac OS X designed to help web authors and application programmers.