WebService Studio 2.0 (a.k.a. Web Service Studio) is a quick & dirty web service client tool that can import your web service's WSDL and allow you to call web service's methods without having to create your own test client.
WebService Studio used to be hosted on Microsoft's GotDotNet web site, but ever since GotDotNet was replaced by Codeplex, Web Service Studio was nowhere to be found. Fortunately, some kind stranger made WSS available for download at his blog: http://mattharrah.com/blog/web-tools/net-web-service-studio-20/.
Update: BTW, if you are planning to use WebService Studio to test WCF web services, you will need to configure your web service to use basicHttpBinding instead of wsHttpBinding.