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 example (last line):

var controller = new AccountController(         // Class I am testing
    mockCustomerRepository,                     // Class I am mocking
    NullObject.For<ILogger>());                 // Who cares about logging!