XML Editors

XML editors provide easier support for editing XML documents with features such as checking for well-formed-ness, validation agains DTDs or schemas and transformations.

firstobject XML Editor
Parse, format, indent, large documents, no Java and no MSXML dependency! Supports incomplete XML documents, even HTML! The firstobject XML Editor freeware edition for Windows provides high performance text editing and parsing of text files. This release is built on CMarkup 8.1 technology to provides light and fast parsing without dependence on external components. The Editor supports aligning and indenting XML, print, print preview, e-mail sending, text encoding selection and conversion, Unicode character functions, and C++ code generation to see how to create or navigate your XML with CMarkup.
[OS: Windows] [Price: Free]
XmEdiL
XmEdiL is free document editor for XML and other languages. Designed for use by professional programmers and novices alike. XmEdiL provides standard Windows interface. Main features: DTD/XML Schema validation, XSL transformations, XPath Builder, W3C specifications conformant, Entry helpers, autocomplete, intellisense, Projects management, Multi-language support (HTML,CSS,JavaScript,VB etc.), Language Editor, Data Import, Customizable syntax colorizing.

XmEdiL has been discontinued and the site (xmedil.com) is no longer available. However, the application is still available for download from some FTP sites. Search for "XmEdiLv.0.4.0.exe" in Google and check the results.
[OS: Windows] [Price: Free] [Note: Discontinued]
Morphon XML Editor
The Morphon XML-Editor is a WYSIWYG Wordprocessor-like validating XML-Editor which lets you easily create and modify XML documents. Morphon also provides a CSS editor for use as a styling language. The Editor itself is multi-platform as it is written in Java.
[OS: Cross Platform] [Price: Free. Used to be $150 but discontinued]
XMLwriter
XMLwriter is an excellent XML editor, which uses the Microsoft MSXML parser by default to validate XML documents against DTDs and XSD Schemas. Validation is also supported for XDR Schemas. If you prefer to use a different parser for validation you can configure 3rd-party parsers. The following file types can be checked for Well-Formedness in XMLwriter: XML, DTD, XSD Schema, and XSLT. Supports XSL Transformation and much more.
[OS: Windows] [Price: $99]
oXygen
The simple and elegant look of oXygen combined with the complete coverage of XML editing features have made it popular in both the corporate and academic worlds. It provides the necessary tools for the document creation and presentation. oXygen XML editor has a large number of features regarding the editing of XML related documents, such as XML schema editing (DTDs, Schematron, etc), XSL/XSLT editor, XSL/XSLT refactoring, XSL/XSLT debugger, XQuery debugger. It is also available as a plugin for Eclipse.
[OS: Cross Platform] [Price: $64 Academic/Home Edition, $225 Professional Edition]
Stylus Studio
Stylus Studio 2006 XML is an advanced XML Integrated Development Environment (XML IDE). Stylus Studio's best-in-class features for working with XML, XQuery, XSLT, EDI, XML Schema/DTD, XPath, SQL/XML, XHTML, and Web services set a new benchmark for XML productivity.
[OS: Windows] [Price: $150 Home Edition, $495 Professional Edition (Compare Editions)]
XML Marker
XML Marker is an XML Editor that uses a synchronized table-tree-and-text display to show you both the hierarchal and the tabular nature of your XML data. It automatically produces a tabular display of any selected tag by collecting repeating attribute and tag names and then arranging them into columns. The result is a clutter-free and informative tabular display.
[OS: Windows] [Price: Free]