Add a login/logout link to a WordPress navigation menu

1. Add the following code to your theme's functions.php file and change the menu area name if you are not using "primary". For WordPress 3.0 and up.

<?php
//Add login/logout link to naviagation menu

function add_login_out_item_to_menu( $items, $args ){


    //change theme location with your them location name

    if( is_admin() ||  $args->menu != 'main-menu' )

        return $items; 


    $redirect = ( is_home() ) ? false : get_permalink();

    if( is_user_logged_in( ) )

        $link = '' . __( 'Logout' ) . '';

    else  $link = '' . __( 'Login' ) . '';


    return $items.= '
'. $link . '
';

}add_filter( 'wp_nav_menu_items', 'add_login_out_item_to_menu', 10, 2 );

/**      END   **/   
?>