JMenu/getItems

To get items of a particular menu:

$menu = &JSite::getMenu(); //initialize menu
/*
 * @param1 attribute used to retrieve data in array $menu
 * @param2 name/filter of attribute
 * @param3 set true to get only the first one menu item, otherwise false get a set of item menu based in your filter and attribute
 */
$menu_desired = $menu->getItems('menutype','mainmenu', false); //get menu items