Put "?=PHPE9568F36-D428-11d2-A769-00AA001ACF42" at the end of any PHP page and then you'll get a picture.

http://forums.krazyletter.com/index.php?=P...69-00AA001ACF42
http://www.helionet.org/index/index.php?=P...69-00AA001ACF42
http://www.dubemail.com/index.php?=PHPE956...69-00AA001ACF42

It really depends on the PHP version on the server, but it usually works. Different PHP versions will have different pictures.

More info here: http://www.0php.com/php_easter_egg.php

Yup, I've heard of this before. I believe PHP 5 doesn't show anything at all.

EDIT
NVM, PHP 5 works too, with the same pic: http://www.zend.com/index.php?=PHPE9568F36...69-00AA001ACF42 (unless Zend is lying about the little PHP 5 logo thing on their website).

Dubemail is on a PHP5 server, too. According to 0php, it is in PHP5, too.