I think this article on a developer's need to output HTML formatted text in one of the new .NET 2.0 web controls is probably one of the better articles on extending a control that I've seen over the past few years.

Clear, concise, and explains a very important aspect of ensuring that you don't destroy needed features while adding new ones to a control.


Of course, on the other hand, I read this CodeProject article and wondered why on earth the author felt that it was worthy of being an article.