XML language
http://www.xmlscript.org/
XMLscript.org is a resource for XML Script, used for manipulating XML data.
http://www.xml.com/
XML.com, where the XML community shares XML development resources and solutions, features timely news, opinions, features, and tutorials; the Annotated XML specification created by Tim Bray; authoring tools, XML developer resources, interactive forums...
http://www.xml.org/
XML.org serves as an online community gathering place for those interested and involved in XML-related standards and specifications.
http://www.zvon.org/
Zvon was founded by a group of people who feel that free information exchange can open new horizons and can be very benefitial for people of similar ideas and needs. Even though Zvon has grown in various ways its original idea is not altered.
http://www.topxml.com/
TopXML, covering all uses of XML in many languages supprting XML, providing working XML sample code, XML tutorials and XML-related references, authoring tools, XML developer resources, XML discussion forums and XML blogs.