This is an incredible wealth of IT resources!  They are all of the sites I have collected from our "guest speakers" in Mark Waddington's Summer 2000 Beginning Networks class at LWTC -along with any randomly mentioned in class or from other classmates in the program.
If the address is indented, although it may be a good site - it did not work when I tried it.  I may have copied it down wrong or the server was down...  If you see a problem with any and know the fix, or just have one to share, please email it to me at kiter6@nwlink.com so I can post it with the next update.
My effort to organize these links is mainly evident at the bottom where I collected a few for the job search and  a section related to security.  -Included are the links from a presentation about security issues by Keith Conners.  I moved the links for the job hunt and added to them at the page linked here and above.

http://ipprimer.windsorcs.com/  Daryl's TCP/IP Primer -Mark gave this one his personal recommendation.
http://www.3com.com/  He called this "a close second."
http://www.blackbox.com/
http://www.searchnetworking.com/
http://www.learntosubnet.com/  "A Free Lecture based Educational Course on IP Addressing and Subnetting"  You can find some practice problems here too.
http://www.whatis.com/
http://www.rad.com/networks/1994/osi/layers.htm
http://www.cableyorkton.com/users/gbraun/batch/

http://support.bagnetworks.com/Library/tpub/html/Routersoft1200/11537Oaa/a_11.htm
http://support.baynetworks.com/library/tpub/html/Router/soft1200/11737Daala_11.htm
http://support.baynetworks.com/library/&pub/html/Router/soft1200/11737Daala_11.htm

http://www.internap.com/ "Based in Seattle since 1996, sells Internet connectivity services.
Provides faster Internet performance using P-NAP (Private Network Access Point).  The P-NAP largely bypasses the public NAPs and private peering points, sending customer data along the shortest, most direct path across the Internet.
An interesting site.  They also have lots of jobs available.
* * * * * (I was referred to this site by my Dental Hygienist)"

http://www.massey.ac.nz/~wwits/services/remote_access/overview.htm  "A university in New Zealand has a good site for information about Remote Access."
http://www.cs.unc.edu/~kimk/atm/  "This site has information about Asynchronous Transfer Mode."
http://www.netsoft.ie/~support/manual/chap3-1.htm  The NET Command
http://www.boson.com/
http://www.sangoma.com/
http://www.powerups.com/
http://www.rad.com/  RAD Data Communications
http://www.lnk.com/
http://www.networkcomputing.com/

http://www.infosecuritymag.com/  Security instructor Mike Curtis recommended getting a free subscription to this magazine.
http://project.honeynet.org/  To learn the tools, tactics, and motives of the blackhat community, and share those lessons learned.  Check out the whitepages link.
http://www.firewallguide.com/  Home PC Firewall Guide
http://www.pgp.com/products/freeware/default.asp  With millions of users worldwide, PGP is the world's de facto standard for email encryption and authentication. This is the only authorized download site...
http://www.bulletproof.com/  The Intranet Application People.
http://ipscan.angryziber.cjb.net/  "the night I checked this out, I was able to easily access three PC's..., scary, very scary..." -from a classmate
http://packetstorm.securify.com/
http://web.mit.edu/pismere/Security/resources.html  NT Security
http://www.securityfocus.com/
http://www.hack-net.com/
http://www.sophos.com/virusinfo/hoaxes/  Before you forward that virus warning "to everyone you know", please check to see if it's a hoax.  Every single warning I've gotten over the years has been on the list of hoaxes.  Also try the last link (www.vmyths.com) from Keith.
 

The first two are the free personal firewalls that Keith mentioned.  Several classmates have told me they installed zonelabs and recommended it.  No system is totally safe if it's on the Internet.  However, it's nice to think that your back door isn't left wide open.
http://www.sybergen.com/
http://www.zonelabs.com/

http://www.nwfusion.com/
http://grc.com/default.htm  Shields up! will scan some of your ports -with your permission.
http://www.mcafee.com/
http://www.norton.com/

This next section was part of Keith's presentation that came from the "commercially influenced" September 2000 issue of PC WORLD at: http://www.pcworld.com/shared/printable_articles/0,1440,17759,00.html
(I made the links hot for your convenience)

 The Internet is a playground for hackers, but it's also a great place to learn about security and how to protect yourself from attack. Here is a sampling of online sites that provide information, testing, and security products.

AntiOnline.com: (www.AntiOnline.com) Provides antihacking and antivirus news and products. It was founded by John Vranesevich, who first praised and later pursued hackers.

CERT Coordination Center: (www.cert.org) Handles security incident response, training, and prevention. Though geared to large-scale networks, the site is loaded with helpful information for PC users.

Gibson Research Corporation: (www.grc.com) Home of Shields Up, a simple Web utility for assessing your system's security risks. Steve Gibson, a software publisher and privacy-and-security advocate, provides plenty of free advice and tips on his extensive site.

HackerWhacker: (www.hackerwhacker.com) Promising to let you "See Your Computer the Way Hackers Do," this site will scan your PC's ports for security vulnerabilities. You can get a one-time scan of most ports for free, or additional and more thorough scans for a sliding fee. We recommend taking the free test run.

HappyHacker: (www.happyhacker.org) The self-described "white hat" hacking site provides loads of information on how to be a hacker and how to protect yourself from one. While it doesn't condone computer crime, the site concedes that its information can be turned to both harmless and devious purposes. A great opportunity to see inside the mind of the hacker.

InfoWorld Security Watch: (www.infoworld.com/opinions ) A regularly updated column on the latest security issues by Stuart McClure and Joel Scambray, authors of the excellent and thorough book Hacking Exposed.

Microsoft TechNet on Security: (www.microsoft.com/technet/security/) Geared to IT professionals (but worth a look for the rest of us), it's a guide to assessing security needs and implementing solutions. Includes updates on viruses and security patches for Windows, Outlook, and Internet Explorer.

Network ICE AdvICE: (advice.networkice.com/) A collection of FAQs, links, and articles on security issues from the company that produces one of our Best Buy products, BlackICE Defender.

SANS Institute (System Administration, Networking, and Security): (www.sans.org) A 96,000-member research and education organization founded in 1989. Its site is loaded with security-related articles. One nifty resource is its list of ports used by Trojan horse programs.

Secure-Me-Automated Security Testing: (www.secure-me.net) This site offers two free port scans: a quick mini "Shield Probe" and a more thorough scan that requires you to wait in a queue, sometimes for more than an hour. Results are e-mailed to you.

VMyths.com (formerly Computer Virus Myths): (www.vmyths.com) Hosted by self-acknowledged dweeb Rob Rosenberger, this site seeks to dispel urban legends about viruses. The first place to go when you get an e-mail warning you of a new virus.