Working with my java colleagues I came to love SOAPUI for testing services. Now Microsoft seems to have catched up with the WCF Test Client. A blog post of dotNET colleague Rick van den Bosch made me search for it in the Common7 folder.
Adding a service is done by putting the URL to the WSDL in the inputbox. So I had to make sure my services expose the WSDL. See below for some configuration options for exposing the WSDL. In both cases the WSDL is exposed on http://SomeMachine/Some/Services/Calculator?wsdl

<!-- Make use of a named behavior configuration -->

<system.serviceModel>
  <services>
    <!-- Service with specified behavior, 
         the behavior contains the address for the WSDL -->
    <service name                  = "SomeService.CalculateImplementation"
             behaviorConfiguration = "CaculateServiceWSDLBehavior" >
      <endpoint
        address                    = "http://SomeMachine/Some/Services/Calculator"
        binding                    = "basicHttpBinding"
        contract                   = "SomeService.ICalculate"
      />
    </service>
  </services>
  <behaviors>
    <serviceBehaviors>
      <!-- Named behavior containing the WSDL URL (httpGetUrl) -->
      <behavior name               = "CaculateServiceWSDLBehavior">
        <serviceMetadata 
          httpGetEnabled           = "true"
          httpGetUrl               = "http://SomeMachine/Some/Services/Calculator" />
      </behavior>
    </serviceBehaviors>
  </behaviors>
</system.serviceModel>

<!-- Make use of baseAddress -->

<system.serviceModel>
  <services>
    <!-- Service with default behavior -->
    <service name                = "SomeService.CalculateImplementation" >
      <!-- baseAddress used for WSDL url -->
      <host>
        <baseAddresses>
          <add baseAddress       = "http://SomeMachine/Some/Services/Calculator" />
        </baseAddresses>
      </host>
      <!-- Endpoint without address, because that is fully 
           specified in the baseAddress -->
      <endpoint
        address                  = ""
        binding                  = "basicHttpBinding"
        contract                 = "SomeService.ICalculate" />
    </service>
  </services>
  <behaviors>
    <serviceBehaviors>
      <!-- Default behavior for every service 
           use of baseAddress needed for WSDL -->
      <behavior>
        <serviceMetadata 
          httpGetEnabled         = "true" />
      </behavior>
    </serviceBehaviors>
  </behaviors>
</system.serviceModel>

Need some online service to get started with WCF Test Client? Check webservicex.