There are hundreds of programmer's sites so I have concentrated on those sites which will be helpful to Win32 assembler programmers. I regularly check out all the sites listed here. I do not link to sites containing unfinished programs, and I only include links to sites which I regard as exceptional.
Wayne J. Radburn's assembler page Learning from one of the pioneers of Win32+assembler. Includes his famous skeleton sample code, and two very useful tools. There is PEView, which enables you to view the internals of exe, dlls, sys, obj, lib and dbg files and thINC which converts Windows "h" files to include files for use with an assembler.
Randall Hyde's WEBster Page Excellent resource centre for the serious assembler programmer, put together by the author of "The Art of Assembly Language Programming" and of the HLA assembler.
T. Schütz's page Great fun and different - see a new angle to Win32 + assembler and lots of regularly updated links.
Kaproncai Tamás' page A well maintained and nicely put together collection of materials and links.
NL Software's Freebyte site Up-to-date links to and information about free tools for the programmer.
The Free Country Another well-maintained and attractive site containing links to free tools for the programmer, and includes recommended books, sources of information etc. Maintained by Christopher Heng.
Assembly Programming Journal An online journal for assembler programmers generally, often with articles about Win32 programming (archive).