Для radio можно, например, так:
<input type="radio" name="browser" value="ie" onClick="f(this)"> Internet Explorer<Br>
<input type="radio" name="browser" value="opera" onClick="f(this)"> Opera<Br>
<input type="radio" name="browser" value="firefox" onClick="f(this)"> Firefox<Br>
<script>
function f(el){
if(arguments.callee.value != el.value){
arguments.callee.value = el.value
alert(el.value);
}
}
</script>