Chad Hovell

Select extra layouts from the post editor Screen Options menu. 
There are now 24 variations to choose from!

Three Column Screen Layout

Three, four and five column screen layouts for the post editor.

David Mosterd

Tobias Schutter

Codepress

Stefan van den Dungen Gronovius

Adds shortcodes to easily create columns in your posts or pages.
Sometimes you just need to divide your page into different columns. With this plugin you just select a column shortcode and it will add the column to the page. You can also change the padding of each individual column from the UI.
There are 10 different column widths available from which you can make all combinations:
<ul>
<li>full width (1/1)</li>
<li>half (1/2)</li>
<li>one third (1/3)</li>
<li>two third (2/3)</li>
<li>one fourth (1/4)</li>
<li>three fourth (3/4)</li>
<li>one fifth (1/5)</li>
<li>two fifth (2/5)</li>
<li>three fifth (3/5)</li>
<li>four fifth (4/5)</li>
<li>one sixth (1/6)</li>
<li>five sixth (5/6)</li>
</ul>
A preset stylesheet is included, which you can also overwrite to you liking in your theme’s stylesheet.
Related Links:
<ul>
<li>http://www.codepresshq.com/</li>
</ul>

Column Shortcodes

Adds shortcodes to easily create columns in your posts or pages.

Three Column Screen Layout vs Column Shortcodes