Pokémon Ruby, Sapphire, and Emerald

Cheats Codes Guides: Pokemon Emerald
Unlockables, passwords, and tips.
http://www.cheatscodesguides.com/gameboy-advance-cheats/pokemon-emerald/

Cheats Codes Guides: Pokemon Ruby
Cheats, unlockables, hints, and Easter eggs.
http://www.cheatscodesguides.com/gameboy-advance-cheats/pokemon-ruby-version/

eLook - Pokemon Sapphire Version
Summary of cheats and codes.
http://www.elook.org/games/cheats/gba/366.shtml

eLook: Pokemon Ruby Version
Summary of cheats and codes.
http://www.elook.org/games/cheats/gba/365.shtml

GameSpy - Pokemon Ruby
Offers game info, cheats, previews, and reviews.
http://gba.gamespy.com/gameboy-advance/pokemon-ruby-version/

GameSpy: Pokemon Emerald
News, screenshots, a review, and a movie.
http://gba.gamespy.com/gameboy-advance/pokemon-emerald/

GameStats - Pokemon Ruby
Contains reviews, news, previews, screen shots, video and popularity ranking.
http://www.gamestats.com/objects/017/017508/

IGN: Pokemon Emerald
Review, news, screenshots, and videos.
http://gameboy.ign.com/objects/692/692344.html

IGN: Pokemon Ruby
Contains reviews, news, guides, cheats, FAQ, game features and message boards.
http://gameboy.ign.com/objects/017/017508.html

Super Cheats
Contains cheats, hints, walkthroughs, GameShark codes, and a message board.
http://www.supercheats.com/gameboyadvance/pokemonruby.htm