Statistic Variables

Hello again everyone... Well, I did create that "visitor log" file for my page, and it's working great, so thanks to all of you that helped me out yesterday! I've been looking and looking and looking through the PHP manual (which for a newbie is very hard to navigate), and I've only come up with a couple of variables that I can use to store information about visitors. $HTTP_USER_AGENT $REMOTE_ADDR And then also the time formatted the way I want it to be. What are some of the other good variables that are commonly used for site access logs, ala "Referred by" and that kind of thing. Thanks! Please CC me, I'm on digest. Martin