I think the Typemock smart way is the best framework for .Net, instead of working in the runtime, it intercepts the CLR and can intercept any call. This allows you to make fun and test anything. Some people find this too powerful. This allows you to test something, while usually the fact that you cannot verify something is a good warning that something is wrong with your design. And it's not free.
I mainly use Rhino Mocks. It has really readable syntax, especially the new AAA syntax. Moq is brand new and should be good, syntax wise. Although I have not tested it yet.
Mendelt
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