Another one starts at
http://www.wwp.brown.edu/outreach/seminars/_current/presentations/xslt/xml_and_xpath_03.xhtml
(click "next" 1/2 dozen times for the effect)
OR
http://www.wwp.brown.edu/outreach/seminars/_current/presentations/xslt/xml_and_xpath.xml#(4)
(just click to go to next 1/2 dozen times for the effect)

This one is affectionately referred to as the "XPath butterfly" for
obvious reasons.

The slides (and, for that matter, all of our materials) are available
under the Creative Commons Attribution-ShareAlike 3.0 (Unported)
license.