Perhaps the best NT related site I know is http://www.jsiinc.com lots of really handy NT info.

http://www.ss64.com/nt/ good command line tips

ISAserver.org - Microsoft ISA Server Resource Site http://www.isaserver.org  news, downloads, articles, 3rd party products, tutorials, newsletters, FAQs, message boards and much more. Also has various FAQs and articles on Windows 2000 security related issues.

WindowSecurity.com - Microsoft Windows security resource site http://www.windowsecurity.com/   Windows security news, articles, tutorials, software listings and reviews for information security professionals covering topics such as firewalls, viruses, intrusion detection and other security topics.

ServerFiles.com - Networking & Server software for Windows 2000/NT & .NET http://www.serverfiles.com/  a software directory for network administrators and IT professionals that are looking for networking & server software for Windows 2000/NT & .NET.

NTfaxFAQ.com - Windows 2000/NT Fax Software Solutions http://www.ntfaxfaq.com A comprehensive and unbiased listing of Fax server software and gateways for Windows NT/2000. Contains detailed information regarding latest fax software for servers.

2000 Trainers has lots of good articles with screenshots on the different functions of 2000 and XP. If you want to learn about windows this is the spot.

Brass Tools and other handy items http://www.ppe.com and http://www.budgetmolders.com have a lot of good hard to find tools.

Raytracings and other fun stuff at http://www.getinfo.net/douge

NTHELP.ORG is another good NT resource with web based support forums. The webmaster is an IIS MVP so it's got lots of good information and a very nice downloads section.

Helmig site has good step by step instructions with screenshots for configuring NT.

NTsysadmin has some good utilities here.

Workstation Weekly has a lot of current type news.

NTadmintools.com (just what it says)

Virtually Unix (unix tools ported to NT)

Tons of NT links here, be prepared to spend a lifetime surfing these.

http://www.systemtools.com/ has some handy utilities and other software for NT.

The NT Game compatibility site is a good place to find out if that game will run on NT.

TechArts Newsletter

Sunbelt NTools E-Newstm Electronic Newsletter

Internet Maps http://www.cybergeography.org/topology_maps.html

www.i386.com has some tips I haven't seen anywhere else

Good tips here www.klcconsulting.net 

Dr HTML - check how good your web page coding is

A new one I just found with lots of registry settings listed http://is-it-true.org/nt

Undocumented Cisco Commands http://boerland.com/dotu

for PC related news, security alerts, etc.