>In particular I'm interested in something that does lots of XPath 
>gymnastics and demonstrates techniques that favour the functional model

>over the procedural model ... and also is comprehensible :-)

Comprehensibility and the necessity of gymnastics are often
diametrically opposed. 
>(and no... don't tell me to buy a book!)
by two books, Jeni's XSLT and XPath On The Edge
http://www.amazon.com/exec/obidos/ASIN/0764547763/104-3990651-4533524
(wish I'd gotten it a year before I did) and Michael Kay's xslt
programmer's reference. The new xslt cookbook might also be worth
getting but I haven't looked at it yet. 

That said:

 
http://www.incrementaldevelopment.com/xsltrick/

http://www.jenitennison.com/xslt/




 XSL-List info and archive:  http://www.mulberrytech.com/xsl/xsl-list