A plugin to show/hide and add elements in the side panel.
I use this solution on our forum, and thought others might find it handy.
Simply, it puts the categories list into a collapsible div, hidden by default, click to show.
Once I got that working, I saw it was fairly easy to add other elements to the side panel using this solution.
Currently for default.master.php files, but I've got it working with a tpl file in 2.1 if anyone wants that.
Demo here: http://www.barspetsa.org/whu606test/
Includes a simple slide option for embedded videos.