<script type="text/javascript">
function getRadioSelectedValue(radioList)
{
var options = radioList.getElementsByTagName('input');
for(i=0;i<options.length;i++)
{
var opt = options[i];
if (opt.checked)
{
return opt.value;
}
}
}
</script>
radioList is the clientid of the radiobuttonlist.
RadioButtonList Javascript Accessible