else if($orderby == 'rand') $ordersql = "  ORDER BY rand()";

else if($orderby == 'idlist') $ordersql = "  ORDER BY FIELD(arc.id,$idlist)";

{dede:arclist idlist='1,2,4,6,10' orderby='idlist'}<li><a href="[field:arcurl/]">[field:id/] - [field:title/]</a></li>{/dede:arclist}