Thanks again to all the people who responded with their excellent suggestions for a new TDD example.
I have decided to choose the Bookmark Collection suggestion from Darrell Norton. Why did I choose this? First it has many of the qualities of the Stack example because on the surface it is a collection. This will allow for most of the interesting discussions that take place around what happens when empty strings or null is passed to the collection. Second, I believe that it can start out simply and become more complicated as new capabilities are added. Lastly, it has the ability to grow into something that could use a database, isolated storage, web service, etc. Evolving the design to meet these requirements will definitely show how to do TDD with these mechanisms.
I will be posting the first task and it's related Test List later in the week.