Some of the sites that you might find useful for additional XSLT information are:
http://www.w3.org/TR/xslt20: The latest version of the XSLT 2.0 specification from the W3C, including references to the other specifications (such as the data model) on which it depends.
http://www.w3.org/Style/XSL/: Home page of the XSL Working Group.
http://xml.coverpages.org/xsl.html: The Cover Pages, run by Robin Cover, provide a comprehensive set of links and summaries of everything in the world of XML and XSLT.
http://msdn.microsoft.com/xml: A good jumping-off point to Microsoft's view on the XML and XSL world.
http://www.mulberrytech.com/xsl/xsl-list: The home page of the xsl-list, a remarkably effective forum for all XSLT matters, from beginners ' questions to advanced theoretical debates.