This function returns an array of timestamp corresponding to Dutch National holidays. Liberation Day (Bevrijdingsdag) is added as a National holiday once every five years (2000, 2005, 2010, ...).

<?php
function getHolidays($year = null) {
    if ($year === null) {
        $year = intval(date('Y'));
    }
    
    $easterDate  = easter_date($year);
    $easterDay   = date('j', $easterDate);
    $easterMonth = date('n', $easterDate);
    $easterYear   = date('Y', $easterDate);
  
    $holidays = array(
        // Nieuwjaarsdag
        mktime(0, 0, 0, 1,  1,  $year),  
        // 1e Kerstdag
        mktime(0, 0, 0, 12, 25, $year),  
        // 2e Kerstdag
        mktime(0, 0, 0, 12, 26, $year)
    );
      
    // Bevrijdingsdag
    if (($year % 5) == 0) {
        $holidays[] = mktime(0, 0, 0, 5, 5, $year);  
    }
    
    // Koninginnedag (< 2014) of Koningsdag (>= 2014). 
    // Verplaats naar zaterdag als het valt op zondag.
    if ($year <= 2013) { // Koninginnedag <= 2013
        if (date('w', mktime(0, 0, 0, 4, 30, $year)) == 0) { // Op zondag?
            $holidays[] = mktime(0, 0, 0, 4, 29, $year);  // Verplaats naar zaterdag
        } else {
            $holidays[] = mktime(0, 0, 0, 4, 30, $year);  // Koninginnedag
        }
    } else { // Koningsdag > 2014
        if (date('w', mktime(0, 0, 0, 4, 27, $year)) == 0) { // Op zondag?
            $holidays[] = mktime(0, 0, 0, 4, 26, $year);  // Verplaats naar zaterdag
        } else {
            $holidays[] = mktime(0, 0, 0, 4, 27, $year);  // Koningsdag
        }
    }
    
    // Onderstaande dagen hebben een datum afhankelijk van Pasen
    // Goede Vrijdag (= pasen - 2)
    $holidays[] = strtotime('-2 days', mktime(0, 0, 0, $easterMonth, $easterDay,  $easterYear));
    // 1e Paasdag
    $holidays[] = mktime(0, 0, 0, $easterMonth, $easterDay,  $easterYear);
    // 2e Paasdag (= pasen +1)
    $holidays[] = strtotime('+1 days', mktime(0, 0, 0, $easterMonth, $easterDay,  $easterYear));
    // Hemelvaartsdag (= pasen + 39)
    $holidays[] = strtotime('+39 days', mktime(0, 0, 0, $easterMonth, $easterDay,  $easterYear));
    // 1e Pinksterdag (= pasen + 49)
    $holidays[] = strtotime('+49 days', mktime(0, 0, 0, $easterMonth, $easterDay,  $easterYear));
    // 2e Pinksterdag (= pasen + 50)
    $holidays[] = strtotime('+50 days', mktime(0, 0, 0, $easterMonth, $easterDay,  $easterYear));

    sort($holidays);
  
    return $holidays;
}

$holidays = getHolidays(2014);

foreach ($holidays as $holiday) {
    echo date('d-M-Y', $holiday) . '<br>';
}
?>

Also, be aware that the eastern orthodox churches sometimes have different dates for easter. See, for example <http://webexhibits.org/calendars/calendar-christian-easter.html>. And note that the dates of easter a subject to change,  for example, the churches might some day decide to unify the dates.