The author makes no assurance that these links are valid, as the Internet tends to change. Additionally, the author has no alliance with any of the contributors or products mentioned here.
Your first resource is the World Wide Web Consortium, http://www.w3.org. There you'll find the latest information about XML and XSL. For more specific information about XML and FileMaker Pro, your Internet travels should lead you to http://www.filemaker.com/xml/ and FileMaker XML Central. There you'll find documents about XML and FileMaker Pro, and links to the FileMaker XSLT Library, FileMaker XML Talk, and recommended books.
Jeni's XML pages—http://www.jenitennison.com/
Patrick J. Kidd's Home page—http://csd1.dawsoncollege.qc.ca/~pkidd/xml_ref.htm
The Web Standards Project—http://www.webstandards.org/
The XML FAQ—http://www.ucc.ie/xml/