IBM DeveloperWorks includes tutorials and other resources on a variety of technologies including Java, XML/XSL, Web Services, WebSphere, Lotus, Linux, Rational, and many others
http://www.ibm.com/developerworks/

o’Reilly’s XML site
http://www.xml.com

XSLT tutorials and resources
http://www.xslt.com

Webmonkey XML topics
http://hotwired.lycos.com/webmonkey/xml/?tw=xml

Site for XML developers. Includes links to other resources.
http://www.xmlhack.com

XSLT spec, tutorial
http://www.w3.org/Style/XSL/

CSS
http://www.w3.org/Style/CSS/

Java tutorial
http://java.sun.com/docs/books/tutorial/

Java, JSP, XML forums and FAQs
http://www.jguru.com

J2EE Community
http://www.theserverside.com

IBM WebSphere Portal Zone
http://www7b.software.ibm.com/wsdd/zones/portal/