We featured the WsContractFirst Add-In in an earlier post, but Christian let me know they have a much improved release of WSCF now. Check out the walkthrough for complete details.
Via smguest: "In short, this tool rocks. It works as follows: You create an XSD using your favorite editor (for example, Visual Studio .NET or XMLSpy) and import it into your Visual Studio .NET project. Right clicking on the XSD in Solution Explorer brings up an option to generate a WSDL file. "