Instance variables in application layout

Hi

I have an application layout, and in it there is a sidebar. What i want to do is put things like tags, newly registered users, recent comments, etc in the sidebar.

I am not sure how to do this...

What controller does the application layout access instance variables from? I presume you can use the application controller, but am not quite sure how...

The controller that is rendering the current action (what other one could it be?).

Fred