<p>I can't seem to find a true restful Blog API - are there any? 
I'm writing some blog software and wondered if there was a standard restful API, if not I'll go buy the RESTful Web Services book and design my own.</p>

How about
AtomPub
?
Atom is the name of an XML-based Web
  content and metadata syndication
  format, and an application-level
  protocol for publishing and editing
  Web resources.
It isn't limited to blogs, but blogs certainly fall under the realm of applications are used for "publishing and editing Web resources".