Kidney Notes sez, "For anyone who's wondered how (or even whether) to cite blogs in formal academic medical papers, the National Library of Medicine/National Institutes of Health provides a style guide. (They used Kidney Notes as one of the examples — I'm honored.)"
KidneyNotes.com [blog on the Internet]. New York: KidneyNotes. c2006 – [cited 2007 May 16]. Available from: http://www.kidneynotes.com/.
(Thanks, Kidney Notes!)