How to remove the Tools menu item from the WP-Admin menu

You want to use remove menu page.

<?php
add_action( 'admin_menu', 'wpse26980_remove_tools', 99 );
function wpse26980_remove_tools()
{
    remove_menu_page( 'tools.php' );
}

You can drop that in your functions.php file (without the opening <?php most likely).

That’s not going to prevent people from typing in yoursite.com/wp-admin/tools.php and seeing the tools page, however.