this is obsolete doc -- see http://doc.nethence.com/ instead

Web Caching 

Apache cache : http://httpd.apache.org/docs/2.2/en/caching.html - http://en.wikipedia.org/wiki/Alternative_PHP_Cache 

Do it yourself in PHP (FR) : http://www.journaldunet.com/developpeur/tutoriel/php/060515-php-cache-serveur-2.shtml 

Alternative PHP Cache (APC) : http://fr3.php.net/manual/en/intro.apc.php 

eAccelerator : http://eaccelerator.net/ 

Xcache : http://xcache.lighttpd.net/