Phrack.org is a security website thats fairly popular out on the web. Their old editions are wonderful for learning all kinds of security tricks, computer hacking, and lock picking. While on the subject of security I found this publication on the dangers and limitation of IMAP security.
Finally a good resource my instructor pointed me to rootvg. Its kinda a mainframe thing but if you check out the “AIX compared (UX, Linux, …)” section you get a great rundown of different *nix setups. Useful for Linux people who wonder how to setup other Unix’ies.