I've been looking around for a collection of sample XML documents and (WD1.0)
stylesheets to render them, but I haven't found any. Does anyone know where I
might find some? I'm looking for some test cases/sanity checks for the
processor I'm working on.

Also, the Proposal for XSL has a section on how an XML document should specify
what stylesheet should be used to render it (see below). Is there a similar
construct in the Working Draft? (I've looked in the document, but perhaps I've
missed it?)

2.2. Referring to a Stylesheet from XML 

The XML WG is defining mechanisms to associate XML documents with stylesheets.
Until this work has been completed, it is recommended that XSL implementations
use the
xml-stylesheet processing instruction proposal. For example, this line would
be included in the XML source file: 

<?xml-stylesheet href="article.xsl" type="text/xsl" ?>

begin:          vcard
fn:             Aneel Nazareth
n:              Nazareth;Aneel
email;internet: anazaret@xxxxxxxxxxxx
tel;work:       x234
x-mozilla-cpt:  ;0
x-mozilla-html: FALSE
version:        2.1
end:            vcard