Puedes ponerlo con un else:
Código PHP:
<?php
$sel_foo = array('candy' => ' selected=""',
'bar' => ' selected=""',
'does' => ' selected=""',
'nothing' => ' selected=""'
);
if(isset($_POST['foo'])){
$sel_foo[$_POST['foo']] = ' selected="selected"';
}
else
{
$sel_foo['candy'] = ' selected="selected"';
}
?>
<select name="foo">
<option value="bar"<?= $sel_foo['bar'] ?>>BAR</option>
<option value="does"<?= $sel_foo['does'] ?>>Does</option>
<option value="nothing"<?= $sel_foo['nothing'] ?>>Nothing</option>
</select>
Salu2,
Carlos.