As a multi-platform blogging tool, iBlogger is an easy candidate for the jack-of-all-blogs award. It offers direct support for 11 platforms, including (alphabetically) Blogger, Blojsom, drupal, ExpressionEngine, LifeType, LivingDot, My.Opera (no, seriously), SquareSpace, TypePad, WordPress, and Xanga, as well as support for other platforms that support either the MetaWeblogs or MovableType APIs. Setup for built-in platforms is about as simple as it gets, though we tested specifically on a WordPress 2.6 blog.
This is based on the Mac OS X desktop application ecto.
I asked for this on the iPhone!