Exiv2

First, of course, Linux.
Stefaan Vanderheyden's Digital Workflow tool, or DigiWf, available on https://launchpad.net/digiwf
Then there's Windows. This one I've already used to view one or two files' XMP data.
LogicMighty (UK) are the "authors," but as they don't link freeware dl's to their homepage, you'll have to settle for a Softpedia link.
-- Checked and works for all XPs plus Vista --
http://download.softpedia.com/dl/ffd6e2e32eeeec95bbd86b2ae5a99e49/4b6863d2/100126403/software/office/InstallXmpExplorer.msi
(Yes, an MSI. No, it doesn't install or arbitrarily start Services, at least not in XP Pro. I know where to check and I have.)

That's my 5 cents.

SJ Wright