Graphical KeyCite for Cases - and soon Legislation
If you haven't tried it yet, give it a look. I think it is vastly easier to interpret the direct history of a case through this pictorial view. For a quick demo, take the jazzy tutorial.
At a law librarian's update today, I learned that Westlaw is planning to introduce graphical KeyCite for legislation as well. A pictorial legislative history - how nifty is that!