The wiki editor with folded templates.
You can unfold the block, by clicking on the arrow to show the template code, or you can click the block and you are presented with a template editor that makes it easier to change the values of the template. This should be very helpful, because research showed that much of the trouble people had with editing Wikipedia, was the complex code on the edit pages. The template code is by far the most obscure and complicated code of all our wiki markup in my opinion. I suspect we will see more of these kinds of additional markup in the editor in the future (headers and links seem like a logical next step).
By clicking the folded Infobox template, you get this template editor.
You might be interested in this video that shows the experience some of the Usability Study subjects were having on the edit page a year ago.