The main sources of information - specifications, references, tutorials, FAQ

XSLT 1.0 W3C Recommendation: http://www.w3.org/TR/xslt

What is XSLT? na XML.COM: http://www.xml.com/pub/a/2000/08/holman/index.html

Mulberrytech.com XSLT Quick Reference (2xA4, PDF): http://www.mulberrytech.com/quickref/XSLTquickref.pdf

Dr. Pawson XSLT FAQ: http://www.dpawson.co.uk/xsl/xslfaq.html

Zvon XSLT Tutorial: http://zvon.org/xxl/XSLTutorial/Books/Book1/index.html