Your question is very generic. And all the methods given above are definite client server techinques. Here are some more.
1. You have a fat client which talks to a database using JDBC/ directly using db protocols . That is a client server communication
2. You use a browser and use http to talk to a
servlet running in a web-app server. That is also client server communication.
3. You use a client which invokes EJBs deployed in an application server.
4. You use RMI
5. You talk to a server directly using TCP or UDP sockets.
6. You talk Http to an web server over a TCP socket...
This list can go on and on. Unless you be a little more specific with your requirements.
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Shubhrajit