• Links - Links to security related sites
• Whois - Information on places to do whois searches.

•  http://www.iana.org/numbers.html  - Internet Assigned Numbers Authority, go to them for IP port number asignments and protocal numbers.
• 32771/tcp and 32772/tcp (IIRC) have been reported to me as Solaris default ports for NIS
• SANS www.sans.org.
• Backdoor trojan ports list www.simovits.com/nyheter9902.html, www.con.wesleyan.edu/~triemer/network/docservs.html, www.con.wesleyan.edu/~triemer/network/regports.html, www.isi.edu/in-notes/iana/assignments/port-numbers.
• RFC search engine www.rfc-editor.org/rfcsearch.html.
• www.opensec.com for security tools.
• www.nessus.org is an open source network security scanner.
• NTP - Network Time Protocol (www.eecis.udel.edu/~ntp/).  Home site of the xntpd time server client and deamon.
• OpenSSH, SSH without the legal strings (www.OpenSSH.com).
• Building Firewall Rule Sets (www.enteract.com/~lspitz/rules.html) by Lance Spitzner.
• Absent (www.research.att.com/projects/absent/) secure remote access from AT&T.  It has a rather nasty disclaimer/license.  Source is provided.  It uses one time passwords in a challenge responce system that you need to use a calculation program to provide the responce.

This computer system is for authorized users only. Individuals using this system without authority or in excess of their authority are subject to having all their activities on this system monitored and recorded or examined by any authorized person, including law enforcement, as system personnel deem appropriate. In the course of monitoring individuals improperly using the system or in the course of system maintenance, the activities of authorized users may also be monitored and recorded. Any material so recorded may be disclosed as appropriate. Anyone using this system consents to these terms.