Is there a standard way of documenting JSP pages?
You could try using <!-- --> to comment! Include HTML <META> tags with a description would work as well. To produce documentation you could write a tool to extract these items to compile documentation.
I did a similar thing to generate end-user HTML doco for tag libraries using XML, XSLT and javadoc -> http://www.ewanharrow.com/java.
The Struts project (part of http://jakarta.apache.org) does a similar thing I believe.