As a Google/GMail user I tend to mainly use Google tools to do a lot of my writing. From Picasa I can write my blog with my photos; from Google Docs I can write my blog as well as normal documents.
For this post, however, I'm using an application that is a beta in the Windows Live suite. You can get Windows Live Writer from here, and I must say it's a very nice blog editor.
The biggest difference between Writer and the many other blogging tools I've tried is that it's like a little local wordprocessor - it is not dependant on being online. That's useful (not essential - ever heard of Wordpad or Notepad?) when you're not connected but still want to put thoughts down and format them ready for publication.