Ranchero Software just introduced MarsEdit which is in 1.0beta. It’s a competitor to other blog posting utilities like ecto.
It was a charm to get working with WordPress after I found instructions online. In fact, this post was written in MarsEdit
Let me quote the instructions for posterity:
In the (excellent) online help there are special instructions for a number of different blogs but there is not one for WordPress.
To get wordpress to work, the rpc url will be the home url plus “/xmlrpc.php”.
The blog-ID should be set to ‘default’ – it seems to hang if you set it to a number (like 1).
Also note that future posts will be retrieved even though they are not yet visible on the blog (in other words the xmlrpc is not filtering – this is not a MarsEdit problem).”