• Moles is a lightweight mocking framework that provides a  mechanism to stub non-virtual methods
• Static methods, methods in sealed types, constructors
• Moles is Delegate based, it provides hooks for the developer to provide their own mock implementation for any dependencies.
• No code refactoring required!
• Moles works in similar fashion as TypeMock, DIF.
• Moles is optimized for Pex. You get the Power of Automated unit tests plus mocking framework.

See here for an example on how to use Moles: http://research.microsoft.com/en-us/projects/stubs/moles.aspx