While researching some information on IMS LOM (Learning Object Metadata), I came across this incredible metadata editor: DC-dot developed by Andy Powell, UKOLN, University of Bath.
You can access it at: http://www.ukoln.ac.uk/metadata/dcdot/
Point it to my blog, and you can see the metadata I've been incorporating into all of my pages! I've been using the Dublin Core recommendation for expressing metadata in html.
The other cool feature, is that it can express the metadata in RDF, as well as convert it to IMS LOM and more!
See also: XML