This is more some investigation for myself, since I wanted to know this. XML attributes that are in (or part of) a recommendation:
xml:lang (heavily used in XHTML documents)
xml:space (the pre element still exists)
xml:base (the base element still exists unfortunately)
Working draft:
xml:id (we should have this now, this makes live so much easier (How should the problem of identifying ID semantics in XML languages be addressed in the absence of a DTD?))
This is all I think, not really sure about this, but hey I have a comment function :-)
See XML and the Web essay, the wild man suggests xml:style, xml:class, xml:href, xml:rel, xml:rev and xml:script !!