Please post here the links to threads that you find exceptionally important of interesting, so that others may find them more easily.

[To moderators: feel free to modify this post to put any additions here and/or remove the no longer needed posts]

X86 ASSEMBLY IN GENERAL:
x86 instruction reference
Fixed point numbers - among others, division by multiplication explained
Big Numbers - working with numbers larger than 32/64 bits, another thread about big numbers
x86-64 Introduction using Intel Manuals (external)

OPTIMIZATION:
MOV vs. XOR vs. AND - zeroing register
AND vs. OR vs. TEST - checking register for zero
Memory copy algorithms
Reverse bits 32
more than one byte NOPs

ADVANCED FASM TOPICS:
Understanding FASM
FASM vocabulary
Porting fasm
Tweaking FASM to allow more instruction/directives per line
Description of multi-pass assembly algorithm
FASM's internal symbol codes (describes the format of parsed source)
Syntax changes in fasm 1.61 and above (introduction of MATCH directive, fixing the FIX, thread started 2005-Jun)

MACRO HELP TOPICS:
Macro tutorials
Macro tutorials -- continuation
Explanation of MATCH directive
Splitting list of symbols

MACRO SOLUTIONS:
Customizing the proc
MASM-like structures and procedures
union macro
for macro
switch/case macros generating jump table
Random number macro
Date/time macros
@@@/@@f/@@b macros
Finite Automata macros
XOR encryption macros
RSA encryption macros
Rijndael (and AES) encryption macros
SHA512 encryption macros
Simple one-section PE encryptor
Extracting resource from external PE file

WICKED FASM MACRO HUMOR:
Simple NASM macrosyntax emulation
FASM solves set of equations
English assembly syntax macros
Compiling .ASM directly into a .TGA image
PE dump done by fasm's interpretive layer
single-line FASM funny programs
interactive assembling
Ada-like syntax
HLL syntax - MessageBox(0, get_name(), "abcd", MB_OK)

OS-DEV:
Entering long (64bit) mode
much on hardware programming [external]
VGA programming
FDC/DMA programming
PCI programming
PCI programming (documentation links)
USB programming
Bootable CDROM code
Accessing HD directly

TOOLS:
FA - command line extension for fasm (2009-Mar / 2009-Aug)
fasm as DLL
Reverend's API resolver (creates import .inc file from DLL)
Decard's ASM2HTML (new version coming soon - decard)
FASM Downloader - fast download latest version of FASM

FASM DEMOSCENE:
cdpod - 512 byte OS, by Dex4U
Smallest sudoku solvers - 1536 byte for win32 by Reverend, 360 byte for DOS by vid
http://board.flatassembler.net/topic.php?t=6010 - 255 byte DOS LFN dir lister, by rugxulo
http://board.flatassembler.net/topic.php?t=5668 - 300byte OS, by kucsikp
http://www.256b.com/ - site containing many 256 byte demos (some in FASM)

OTHER:
FASMARM - FASM clone for ARM processors
Macros for AVR (ATMEL) microcontrollers programming
Neural64 - self-learning neural network example
PIC code with ELF format - creation of shared libraries in Linux
Flat Real/unReal mode
equivalent for GNU AS .balign
TextPad - Using TextPad with FASM
Hypervisors - theory on creating hypervisors
Updating instruction microcode

Server side applications

• The Asm_CGI Tutorial (external site, dead)
  
• CGI without C or Perl in ASM

Two 256b VGA intros w/ src (Boxes, Astroids 2) -- Grenhald

Para512: 512b paratrooper w/ src -- vid

"regression...": three 256b demos w/ src (Flower256, Bounce256, Wobble256) -- relsoft

P.S. I hate to link to my own stuff, but anyways ... tiny .ZIP viewers (106 bytes -> ATV; 122, 254 bytes -> me)

Misc. demo URLs (not necessarily for FASM):
http://www.pouet.net
http://www.scene.org
http://www.frontiernet.net/~fys/hugi/hcompo.htm
http://www.hugi.scene.org/compo/ (has newer 64-byte compo entries)

: http://www.256b.com - dead
:

That sucks, I liked that site....good thing I have the whole archive downloaded.

SOME MORE INTERESTING THREADS :
I would edit this post if I find any interesting ones.
8 byte drawing algorithm by bitshifter (total 17 bytes ) <--- This is amazing.
http://board.flatassembler.net/topic.php?t=9147
EDIT:
m3ntal's Sprite Fight Game http://board.flatassembler.net/topic.php?t=16197
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Shows powerful usage of macros! (For those who're lazy to code in assembly, and see how macros work, this is recommended. Also has decent graphics. )
Sprite Editor for DOS by lutetia -
http://board.flatassembler.net/topic.php?t=14875
Fire Flame Animation by Dex4u in VGA Mode 13h -
http://board.flatassembler.net/topic.php?t=12456
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Nice for an intro for your proggy....
FunOpenGL beautiful graphics game by tthsqe: http://board.flatassembler.net/topic.php?t=15746

Get the ultimate intros collection and enjoy:
hardcode.zip (376 MB)
Download it at: http://hardcode.untergrund.net