<select onchange="for(var i=0;i<s2.length;i++){if(s2.options[i].text==this.options[this.selectedIndex].text)s2.options[i].selected =true;}">
<option>aaa
<option>bbb
<option>ccc
</select>
<select name=s2>
<option>bbb
<option>aaa
<option>ccc
</select>