<select onchange="check(this)">
<option>...</option>
<option value="1">1</option>
<option value="2">2</option>
<option value="coding123.net" linkto="http://www.coding123.net">coding123.net</option>
<option value="3">3</option>
</select>
<script type="text/javascript">
function check(s){
  var opt=s.options[s.selectedIndex];
  if(opt.getAttribute('linkto'))top.location=opt.getAttribute('linkto')
}
</script>

------解决方案--------------------
探讨

添加onchange事件，判断是否有linkto

HTML code
<select onchange="check(this)">
<option>...</option>
<option value="1">1</option>
<option value="2">2</option>
<option value="coding123.net" linkto="http://w……