Over on IBM developerWorks, Elliotte Rusty Harold takes an introductory look at some of the new elements which will be part of the HTML 5 specification:

"New elements in HTML 5" - http://www.ibm.com/developerworks/library/x-html5/?ca=dgr-lnxw01NewHTML

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Updated 2021 : note that the above post was originally published in 2007, but is left here for archival purposes. The external link is now dead so I have unlinked it.