A list of resources follows.
BSD Hacks, Dru Lavigne (O'Reilly), 2004
FreeBSD release engineering: http://www.freebsd.org/releng/
FreeBSD mailing lists: http://www.freebsd.org/support.html#mailing-list
OpenBSD flavors: http://www.openbsd.org/faq/faq5.html#Flavors
OpenBSD mailing lists: http://www.openbsd.org/mail.html
Unix Backup and Recovery, W. Curtis Preston (O'Reilly), 1999
Big Brother: http://www.bb4.com/
Big Sister: http://bigsister.graeff.com/
Nagios: http://www.nagios.org/
OpenNMS: http://www.opennms.com/
Incident Response, Richard Forno and Kenneth R. van Wyk (O'Reilly), 2001
SecurityFocus: http://www.securityfocus.com/
SSH, The Secure Shell: The Definitive Guide, Daniel J. Barrett and Richard Silverman (O'Reilly), 2001
Topics in Cryptography: http://www.wikipedia.org/wiki/Topics_in_cryptography