Tom at Backup Brain posts:
Kung-Log is a Mac OS X application that lets you post and manage Movable Type entries. Written with AppleScript Studio, I believe.
I downloaded this a while back but haven’t had a chance to test it out yet.
I recall that Scot Hacker also told me a while back that iJournal, an OS X app for posting to LiveJournal can in theory be extended to post to any blog (I’m not sure how all these things work!). Then there’s w.bloggar, an app for Windows that posts to a number of different blogging systems.