Spec# for Visual Studio 2005 is out now… Perhaps, we will see this along with Pex in the version of VS following Orcas. Here’s the description of Spec# in the Microsoft Research site:

Spec# is an experimental language that extends C# with several design-by-contract features. The new features of Spec# include a non-null type system, method pre- and post-conditions, loop invariants, and object invariants. The Spec# Programming System provides design-time checking, run-time checking, and a static verifier. This version of Spec# runs on .NET Framework version 2.