I usually post directly into the WP dashboard. Using spell check and swapping back in and out of html view. I originally tried to use open office but found with copying and pasting I had lost a lot of my original formatting. So far I've found it to be quite efficient.
I used to compose in Notepad, but found composing directly in the dashboard easier. I have an addon for Firefox that checks spelling mistakes, so I don't need a third-party spell checker.
I sometimes write my posts ahead of time, and then schedule them for later.