Tags as autocomplete values

if(isset($_GET['get_tags'])):
  $output = array();
  foreach(get_terms('post_tag') as $key => $term):
    // filter by $_GET['q'] here if you need to,
    // for eg. if(strpos($term->name, $_GET['q']) !== false)...
    $output[$key]['value'] = $key;
    $output[$key]['name'] = $term->name;
  endforeach;

  header("Content-type: application/json");
  echo json_encode($output);
  die();
endif;

in this case your js would be something like:

$("#input_1_3").autoSuggest(
    "http://yoursite.com/?get_tags=1",
    {selectedItemProp: "name", searchObjProps: "name"});