Very good editor for structured documents (like DocBook XML). DTD-only version is free to use and comes with DocBook support. XML Schema enabled version is commercial available.

Cross-platform and multi-purpose XML editor, XSLT debugger and Visual Schema Editor. Provides editing support for XML, DTD, XHTML, XSLT, XSD, XML RelaxNG, SVG, MathML and XSL FO [Commercial, 30-day trial].

An XML editor for data oriented documents. Editing is guided by any DTD or RELAX NG schema. [Open Source, BSD-like]

Cross-platform XML and XSLT Manager. [Shareware]

A Java-based XML editor that facilitates easy browsing, editing, managing and conversion of XML documents. By Cladonia Ltd. [Commercial]

Tools for building XML-enabled Java/J2EE applications, including a JSP 1.0/2.0 editor, Java IDE, support for Java XML components including Xalan, Xerces, Saxon, and Java Web services. [Commercial]

A graphical Java XML editor customizable with an XML schema and a file describing the menus to insert the elements. [Open source, GPL]

Generic Java application for editing valid XML documents derived from any valid DTD. (IBM Corporation)

Java-based XML editor that supports DTD validation. [Commercial]

An extensible Java based XML editor. [Open source]