I am not a web programmer, so please excuse my ignorance. When it comes to server side programming, we have plethora of technologies available, such as PHP, ASP.net, JSP and so on.
However, when it comes to client side scripting, I have only heard of JavaScript and AJAX. Maybe you can also include Java Applets, as they run on the client. A relatively new one is also the Google's native client. But are there any more client side technologies which exist and are popular?