<input type="submit" class="superbutton" name="pay_mode" value="20" />
<form action="?action=select_pay" method="POST">
<input type="hidden" name="pay_mode" value="20" />
<input type="submit" class="superbutton" value="Яндекс Деньги" />
</form>
<form action="?action=select_pay" method="POST">
<input type="hidden" name="pay_mode" value="10" />
<input type="submit" class="superbutton" value="Еще одна платежка" />
</form>
<input type="hidden" name="pay_mode" value="20" />
<input type="submit" class="superbutton" value="W1 касса" />
<input type="hidden" name="pay_mode" value="15" />
<input type="submit" class="superbutton" value="Яндекс Деньги" />
<input type="submit" class="superbutton" value="Яндекс Деньги" data-transfer="20" />
$('input[type=submit]').click(function() {
$(this).val($(this).attr('data-transfer'));
}
<?
if (isset($_POST['page']))
echo $_POST['page']."<br/>";
?>
<!DOCTYPE html PUBLIC "-//W3C//DTD XHTML 1.0 Strict//EN" "http://www.w3.org/TR/xhtml1/DTD/xhtml1-strict.dtd">
<html xmlns='http://www.w3.org/1999/xhtml'>
<head>
<title>Тестовая страница</title>
<script type='text/javascript'>
function sub(action){
if (action == 1)
window.document.getElementById('page').value = "20";
else
window.document.getElementById('page').value = "30";
window.document.getElementById('form').submit();
}
</script>
</head>
<body>
<form method='post' action='' id='form'>
<input type='hidden' name='page' value='1' id='page'/>
<input type='button' value='Яндекс деньги' onclick='sub(1)'/>
<input type='button' value='W1' onclick='sub(3)'/>
</form>
</body>
</html>