EXcelon Stylus Studio
The stylus studio xml editor is an innovative xml ide providing advanced xml development tools for xml, xsl, xslt, xml schema, dtd, soap, wsdl, sql/xml, xml mapping, web services and xquery, simplifying xml data integration.
http://www.stylusstudio.com/
IBM XSL editor
A visual xsl stylesheet editor that combines the ease of a wysiwyg tool with the power of xslt.
http://www.alphaworks.ibm.com/tech/xsleditor