<?php if ( ! defined('BASEPATH')) exit('No direct script access allowed');
// sample code for thread http://expressionengine.com/forums/viewthread/174318/
class Accessory_test_acc
{
   
   public   $name           = 'Test Accessory';
   public   $id             = 'accessory_test_acc';
   public   $version        = '1.0.0';
   public   $description    = 'Test bed for accessories';
   
   function Accessory_test_acc()
   {
      $this->EE =& get_instance();      
   }
   
   public function set_sections()
   {
      // Add some stuff to the head (you could alternatively load a js file from your add-on package)
      // @see http://expressionengine.com/user_guide/development/usage/cp.html#add_to_head
      // @see http://expressionengine.com/user_guide/development/usage/cp.html#load_package_js  
      $this->EE->cp->add_to_head("
      <script type='text/javascript'>
         $(function() {
            // .bind() documentation: http://api.jquery.com/bind/
            $('#my_ajax_link').bind('click',function(e){
               e.preventDefault();
               // $.load() documentation: http://api.jquery.com/load/
               $('#my_ajax_box').load($(this).attr('href'),function(){
                  // $.dialog() documentation: http://jqueryui.com/demos/dialog/
                  $('#my_ajax_box').dialog({
                     modal: true,
                     title: 'Howdy',
                     buttons: {
                        Ok: function() {
                           $(this).dialog('close');
                        }
                     }
                  });
               });
            });
         });
      </script>
      ");
      
      $this->sections['Test One'] = "<p><a id='my_ajax_link' href='".BASE.AMP."C=addons_accessories&M=process_request&accessory=accessory_test&method=process_ajax&id=232'>Click this to test the ajax return</a></p><div id='my_ajax_box'></div>";

   }
   
   public function process_ajax()
   {
      // Check to make sure it's an ajax request - if not we return a user error for this example
      if (isset($_SERVER['HTTP_X_REQUESTED_WITH']))
      {
         // normall I'd build this in a view file using $this->EE->load->view('file',$data,TRUE)
         // but I can't seem to load a view inside these accessory methods. See this for details:
         // http://expressionengine.com/forums/viewthread/175547/
         // http://expressionengine.com/bug_tracker/bug/14741/
         
         $out = "<div style='margin-top:10px'>";
         $out .= "<p>This content is coming from within my <pre>process_ajax()</pre> method of the accessory.</p><br/>";
         $out .= "<ul>";
         // Simulate some data coming from the database or something - we'll just use a basic array
         $array = array("one","two","three","four","five");
         foreach ($array as $result) {
            $out .= "<li>{$result}</li>";
         }
         $out .= "</ul>";
         $out .= "</div>";
         exit($out);
         // exit(file_get_contents(dirname(__file__).'/views/entry_info.php'));
      } else {
         return $this->EE->output->show_user_error('general','Javascript is not enabled (apparently)');
      }
   }
   
}

https://gist.github.com/736150

Sample accessory with ajax method for EE 2.x

ajax, javascript, php, jquery

PHP