http:*//www.pepysdiary.com is posting the entire diaries of Samuel Pepys, who recorded much of the events during the English Restoration period. They are posting the blog at one entry per day, with the entry from 1/1/1660 posted on 1/1/2003. Seems like an interesting use for the blog format.
The closest blog that I've seen to the Pepys diary is Bloggus Caesari (http:*//www.sankey.ca/caesar/index.html) where Julius Caesar tells of his military life.