How about

$html .= qq{<select name="my_parameter">\n};
for my $option ( ['option1', 'Option 1'],
                 ['option2', 'Option 2'],
                 ['option3', 'Apple pie']  ){
 if ($option->[0] eq $existing_value){
  $html .= qq{<option value="$option->[0]" selected>$option->[1]</opti
+on>\n};
 }else{
  $html .= qq{<option value="$option->[0]">$option->[1]</option>\n};
 }
}
$html .= "</select>\n";
[download]

The inside could be rewritten as:

 $html .= qq{<option value="$option->[0]"} .
                 ($option->[0] eq $existing_value ?
                  ' selected' : '') .
                 qq{>$option->[1]</option>\n};
[download]

And you should think about using entities, 'cause an $existing_value with a " in it isn't going to make you happy...

2;0 juerd@ouranos:~$ perl -e'undef christmas'
Segmentation fault
2;139 juerd@ouranos:~$
[download]