Programming

OSR Open Systems Resources, Inc.
Windows NT device driver and file systems experts. Custom development, worldwide public and private training seminars, newsletter and consulting.
http://www.osr.com/

Sam Blackburn's Win32 Foundation Classes
WFC offers C++ programmer functionality, wrappers for unwieldy NT features such as access control, CryptoAPI, event log, RAS, and services.
http://www.samblackburn.com/

Systems Internals
System utilities for Windows NT and Windows 95/98. Includes NTFS driver for DOS, FAT32 driver for NT and NT Undelete program, most with source code. Very good for system administrators and system programmers.
http://www.sysinternals.com/

Tomas Restrepo's WinDev
Offers code and articles on I/O Completion Ports, including a C++ template class for IOCPs; network services; threads; and synchronisation objects.
http://www.winterdom.com/dev/

Win32 samples
Sample code for some aspects of NT programming, mostly from the areas of security and networking, such as Net*() APIs and IOCPs (I/O completion ports) with sockets.
http://mvps.org/win32/

Windows 2000 Developer Center (MSDN Online)
The one-stop for all developer information about Microsoft Windows 2000.
http://msdn2.microsoft.com/en-us/library/aa286534.aspx