dexxaye

This plugin allows user to add additional columns to admin posts and pages page. 
Now supports custom post type

Custom Admin Columns

This plugin allows user to add additional columns to admin posts and pages page.

grnesmith

This Plugin adds the ability to change the vertical screen columns on the admin dashboard. To make a change to the amount of columns displayed click the screen options drop down and select the number of columns under screen layout.

Admin Column View Selector

This Plugin adds the ability to change the columns on the admin Dashboard screen.

Custom Admin Columns vs Admin Column View Selector