The XML Bible
Elliotte Rusty Harold
IDG Books, 1999
ISBN: 0-7645-3236-7
Chapter 14, XSLT: http://www.ibiblio.org/xml/books/bible/updates/14.html
XML in a Nutshell
Elliotte Rusty Harold and W. Scott Means
O'Reilly & Associates, 2001
ISBN 0-596-00058-8
Chapter 9 XPath: http://www.oreilly.com/catalog/xmlnut/chapter/ch09.html
This presentation: http://www.ibiblio.org/xml/slides/sd2001west/xslt
XSL Transformations 1.0 Specification: http://www.w3.org/TR/xslt/
XPath Specification: http://www.w3.org/TR/xpath