I have added this CrmDiscoveryService Web service reference:
http://<servername:port>/mscrmservices/2007/ad/crmdiscoveryservice.asmx?WSDL
But still cannot see CrmDiscoveryService type in Intellisense.
(I am working with CRM 4.0 and VS 2012 in C#.)
When you add a Service Reference, go to "Advanced" In the first dialog window, then click "Add Web Reference" on the bottom of the page. On the next page you can add your web reference...