MASM32
Home of the MASM32 distribution. MASM32 contains the Microsoft Macro Assembler and related files required for WinAsm Studio.

Catch22 Productions
An online resource for Win32 software, sourcecode and tutorials

The GeneSys Project
Aimed to help coders who are making their first steps in the assembly language.

OllyDbg
OllyDbg is a 32-bit assembler level analysing debugger for Microsoft� Windows�. Emphasis on binary code analysis makes it particularly useful in cases where source is unavailable. OllyDbg is a shareware, but you can download and use it for free.

GRDB
GRDB is the 'Get Real' real mode debugger for x86. You can use it to debug 16-bit applications.