<?php
if($location != "")
header("Location: $location");
else
{
echo "
<body>
<form action=\"$PHP_SELF\" method=GET>
<select name=\"location\">
<option value=\"http://www.somesite1.com\">Site1</option>
<option value=\"http://www.somesite2.com\">Site2</option>
</select>
<input type=\"submit\" value=\"Go\">
</form>
</body>
";
}// end else
?>
I think that should work although I havent tested it. If you want more options just foloow the example.
Hope this Helps!