codice:
function f(){
 var d=new Date();
 var g=parseInt(d.getDate());
 var m=parseInt(d.getMonth()+1);
 var a=d.getFullYear();
 if(g<10) g="0"+g;
 if(m<10) m="0"+m;
 document.nomeform.nomeselect.options[document.nomeform.nomeselect.options.length]=new Option(g+"/"+m+"/"+d.getFullYear(),g+"/"+m+"/"+d.getFullYear());
}
da usare così:

codice:
<body onload="f();">
ciao