Code Contracts Editor Extension
Bake the Code Contracts Editor Extension into Visual Studio, with less bugs, better performance and more features.
Adam Speight commented
Make it support VB.net as well.
It would be nice to see some refactorings around contracts as well; such as adding basic checks for null or generating a contract class for an Interface. A more complex refactor to convert existing ArgumentExceptions to a Contract expectation would be great too as well as documentation generation.