Sidebar
If you've got a a lot of content or a very short sub menu on a page, you may find yourself thinking, 'hey, what about that perfectly useful column space below the sub menu? Why can't I put stuff in there?'
To which we would answer, 'you can. Just put it in the side bar box.'
One thing to remember with the side bar is that it's not a very wide space. If you put a normal sized inline image in there, for instance, it would get cropped (although thumbnails and icons will fit just fine).
You can use any of the normal content markup in the side bar.