<select id="selectlist" name="selectlist">
<?php
$somearray = array("option1" => "label1", "option2" => "label2", etc);
foreach ($somearray AS $key => $value) :
echo "<option value='".$key."'".($key == $_POST['selectlist'] ? ' selected="selected"' : '').">".$value."</option>\n";
endforeach;
?>
Then if you put the array at the top of the page (or in a config file if it's used on multiple pages), you could, in your form processing/checks do
if (!empty($_POST['selectlist']) && in_array($_POST['selectlist'], $somearray)) :
// okay to proceed
endif;
Am sure there is probably a better way to do all of this but it cuts down large chunks of html and unnecessary repeats with long select lists (anything over 3 options I tend to use the above method).