Both Michael Kay's and Jeni Tennison's book already mentioned are good
choices. Jeni recommends Michael's book as a reference, but she is a
generous person. I would read anything she wrote.
XSLT is not easy to learn. For starters, there are two languages: the outer
XML syntax language of templates and constructors, and the inner XPath
language used for matching, expression evaluation, etc. Perhaps for this
reason, it is an indisputable fact that, while you can do anything with
XSLT, most people do not find it obvious how.
If you want online references, here are some in both categories:
Microsoft has a decent "just the facts" reference breakdown:
http://msdn.microsoft.com/library/default.asp?url=/library/en-us/xmlsdk/htm/sdk_intro_6g53.asp
On this page there are links to both XSLT and XPath references. You'll need
both.
Jeni Tennison's XSLT website has lots of "how to" material.
http://www.jenitennison.com/xslt/
The ultimate "do anything" reference has to be Dimitre Novatchev's work on
functional programming in XSLT:
http://www.topxml.com/xsl/articles/fp/
This is for people who have a solid background in both functional
programming and XSLT; not the place to learn either one.
Finally, comp.text.xml is not the best place to ask XSLT questions. You
should subscribe to xsl-list
http://www.mulberrytech.com/xsl/xsl-list/
At first, just read the traffic going by, esp. Michael Kay's and Jeni
Tennison's responses.
Bob Foster