Windows Live Writer is one of the best programs for allowing you to author posts for your WordPress blogs. This one utility which is free and provided by Microsoft is so full featured that you will never find yourself using Microsoft Word, Notepad or Wordpad again to write blog posts.
Windows Live Writer allows you to write in both visual mode, html mode and see a live preview of what your post will look like on your blog. Live Writer imports your WordPress blog theme so that you can write content and see exactly how it will look when published while you are writing it.
Here is my video demonstration showcasing Windows Live Writer for WordPress (it is worth the 12 minutes to watch).
You can not only add text, html code, but from Live Writer you can manage tags, slug, excerpt, scheduled date, save drafts, insert images (including sizing, margins, text wrap) that will automatically upload when you publish your post or save it as draft to your WordPress blog.
Windows Live Writer can also allow you to seamlessly switch a blog post from one blog to another if you would rather change which blog your post should be published on. It allows instant hyperlink creation with adding rel="nofollow" and even allows you to create html tables and embed YouTube videos with the click of a button and copy/paste of a URL.
Personally Windows Live Writer allows me to blog more efficiently as I do not have to do as much editing in the WordPress editor when creating my content with Windows Live Writer. Combined with the fact that you can write all of your content offline and just schedule and publish it when you get reconnected to the Internet allows you to write content for your blog anywhere you go.
I highly recommend Windows Live Writer if you have not downloaded and taken a look at the software before.