devrs.com - GBA programming information and news
GBATek - the ultimate GBA technical reference document
gbadev.org - documention, demos and tools
VisualBoy Advance - Gameboy Advance emulator
GBA Pollution - Home of Ditty Editor and Tile Quant Do
Cearn Space - GBA tutorials and useful tools
SGADE - Socrates Gameboy Advance Development Engine
Dooby's GBA Resources - Useful tools and examples
FireFly's E-reader Resources - Useful tools and examples
Chishms projects - including the gba & nds FAT library

FireFly's eReader site. - tools and docs for eReader programming.
Caitsith's eReader site.

gcdev.com - documentation, demos and tools
Dextrose Gamecube Forums
WhineCube - Gamecube emulator
Dolphin - Gamecube emulator
Dolwin - Gamecube emulator

NDSTech Wiki
doublec - NDS development tutorials
Dualis - NDS emulator
DSemu - NDS emulator
Ideas - NDS emulator
NDSHB - Nintendo DS homebrew ROMs and reviews.
DS Lua - Lua library for the Nintendo DS.

devrs.com - GP32 programming information and news
GP32 Xtreme - news, reviews and discussion boards
Mirko's SDK - replacement for the official Gamepark SDK

UltraEdit - one of the best code editors around
Dead coders society - NGPC, GP32, WSC, GBA, GC and Zodiac Development Pages
The Pern Project - tutorials for console programming
MinGW - Minimalist GNU for windows
Torlus' Console Development - GBA, GC and NeoGeo Pocket development
Ranjit Mathew's home page
Mumit Kahn's home page
DesktopMan's homepage - tutorials, documentation and example source
PinEight.com - source code and informative articles by Damian Yerrick
Dead Coder's Society - Gaming Console Development Pages

WarioWorld - Official Nintendo developers
Kraln.com -
Darkain.com
StoneCyph - ramblings of the #gbadev resident psycho.

DevkitARM - discussion and announcements for the ARM devkit
DevkitPPC - discussion and announcements for the PPC devkit
DevkitPSP - discussion and announcements for the PSP devkit
GBAdev - discussion of Gameboy Advance development
GP32dev - discussion of Gamepark GP32 development