You can use button_to_function with remote_function to create a button that will use Ajax to call an action in your controller.
The method remote_function takes the same parameters as link_to_remote, which means that you can then use parameters like :before, :after, :complete, etc. to call arbitrary JavaScript at various points during the Ajax request.
For example:
<%= button_to_function("Click me", remote_function(:url => {:action => :do_stuff}, :before => "myJavaScriptFunction()")) %>
Chris
