...take the XML Notepad.

"Handy features include:

• Tree View synchronized with Node Text View for quick editing of node names and values.
• Incremental search (Ctrl+I) in both tree and text views, so as you type it navigates to matching nodes.
• Cut/copy/paste with full namespace support.
• Drag/drop support for easy manipulation of the tree, even across different instances of XML Notepad and from the file system.
• Infinite undo/redo for all edit operations.
• In place popup multi-line editing of large text node values.
• Configurable fonts and colors via the options dialog.
• Full find/replace dialog with support for regex and XPath.
• Good performance on large XML documents, loading a 3mb document in about one second.
• Instant XML schema validation while you edit with errors and warnings shown in the task list window.
• Intellisense based on expected elements and attributes and enumerated simple type values.
• Support for custom editors for date, dateTime and time datatypes and other types like color.
• Handy nudge tool bar buttons for quick movement of nodes up and down the tree.
• Inplace HTML viewer for processing xml-stylesheet processing instructions.
• Built-in XML Diff tool.
• Support for XInclude
• Dynamic help from XSD annotations.
• Goto definition to navigate includes and XSD schema information. "

Source: http://www.microsoft.com/downloads/details.aspx?familyid=72d6aa49-787d-4118-ba5f-4f30fe913628&displaylang=en