<!DOCTYPE HTML>
<html>
<head>
<meta charset="utf-8">
</head>
<body>
<form>
<input class="clear" type="hidden" value="234" default-value="234111">
<input class="clear" type="text" value="2345" default-value="2345">
<textarea class="clear" default-value="25">25</textarea>
<input type="button" value="reset" onclick="resetForm(this)">
</form>
<script type="text/javascript" src="http://code.jquery.com/jquery-1.10.2.min.js"></script>
<script type="text/javascript">
function resetForm(a) {
a = a.parentNode.getElementsByClassName('clear');
for(var i=0; i<a.length; i++) if(b) a[i].value = a[i].getAttribute('default-value');
}
</script>
</body>
</html>
Без jQuery. Не проверял, но работать должно.