This should be easy enough, just add more urls if you wish
<?PHP
srand((float) microtime() * 10000000);
$url_list = array("http://site.com",
"http://site2.com",
"http://site3.com",
"http://site4.com",
"http://site5.com");
header('Location: '.$url_list[rand(0,count($url_list))]);
?>