This NullObject Factory from Paul is very nice, simple and clean in its design. I really like it and I can see many uses for it, in parallel with working with your standard mocking framework or IoC Container Implementation . here is a little usage
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Read the complete post at http://weblogs.asp.net/rosherove/archive/2008/05/10/nullobject-for-lt-t-gt-as-simple-as-it-gets-but-no-simpler.aspx