GameSpot: Yu-Gi-Oh! Duel Monsters II Released only in Japan. Includes hints. http://www.gamespot.com/gbc/rpg/yugiohduelmonsters2/

GameSpot: Yu-Gi-Oh! Duel Monsters 4 Contains cheat codes, FAQs, and user reviews. http://www.gamespot.com/gbc/rpg/yugiohduelmonsters4kd/

GameSpot: Yu-Gi-Oh! Duel Monsters 6 Expert 2 Includes user reviews, cheat codes, and FAQs. http://www.gamespot.com/gba/rpg/yugiohduelmonsters6expert2/

GameSpot: Yu-Gi-Oh! Duel Monsters 7: Kettou Toshi Densetsu Offers cheat codes, FAQs, and user reviews. http://www.gamespot.com/gba/rpg/yugiohduelmonsters7ktd/

GameSpot: Yu-Gi-Oh! Shin Duel Monsters 2 Includes FAQs and reader reviews. http://www.gamespot.com/ps2/rpg/yugiohshinduelmonsters2/

eLook Provides codes for the Game Boy Advance version. http://www.elook.org/games/cheats/gba/444.shtml

GameFAQs Provides information, reviews, FAQs, guides, codes, secrets, and a message board. http://www.gamefaqs.com/portable/gbadvance/data/30515.html