Ayende has announced that he's released Rhino.Mocks v. 2.0: his own version of what he'd like in a Mock Object framework. I haven't yet got a chance to try it out, but it certainly sounds interesting!
"Rhino.Mocks is an attempt to create easier way to build and use mock objects and allow better refactoring support from the current tools. It's a hybrid approach between the pure Record/Replay of EasyMock.Net's model and NMock's expectation based model. Rhino.Mocks originated from EasyMock.Net and attempt to improve on their model to create easy to use and power mocking framework. It's free for use and modification for free and commercial software.
I created Rhino.Mocks because I wanted better support from refactoring tools such as ReSharper and because I don't like the way NMock handle parameterized methods (you need to pass fake constraints to get it to recognize the correct method) and the lack of extensibility [I required hacks to get to the result that I wanted]."