I finally finished the 3 column version of SEO Simple WordPress Theme.
The layout is such that the post area appears to the left of the screen and two sidebar columns are at the right. This provides a bit more space for adding more links and adverts and other bits and pieces.
You can see the regular and 3 column themes in action here. I have added a theme switcher so that you can toggle between them both.
UPDATE: This theme is outdated. Sadly, I do not update it anymore. I hope everybody who used it enjoyed it. The download link has been removed permanently.