For SSI, try:
<!--#exec cmd="date +'%A, %B %d, %Y'"-->
A little more information about the date command:
http://www.rt.com/man/date.1.html
For PHP, try:
<?php echo date("D F j, Y"); ?>
A little more information about the php date function:
http://www.php.net/manual/en/function.date.php