These are few and far between. Even when you think you've run into something truly unique, visit the actual thread and forum pages, and you'll find all that was really different was the custom wrapper of the site. This might be due to a desire to keep the discussion forums familiar and out of a fear that doing something too different will take away from that. And part of it might be due to the fact that people prioritize function over form. Personally, I think we should have both. And I'm working on some skins right now in an attempt to change that.
This is a work-in-progress, which is why you might see some orange contrast in there. Why it differs should be pretty self-explanatory.
Attachment 144208
More high res view
here.