FF3man's Final Fantasy III/VI Castle

Fan fiction, character pictures and information, item lists, downloadable icons and music, a visitor poll and a message board.
http://www.geocities.com/ff3man

GameFAQs: Final Fantasy III (SNES)

Features user-submitted FAQs, guides, walkthroughs, codes, save files, and reviews as well as a messageboard.
http://www.gamefaqs.com/console/snes/data/8998.html

RPG Dreamers

Features reviews, FAQs, codes, music in MIDI format, images, main character profiles with illustrations, and a forum link.
http://www.rpgdreamer.com/ffa/ff6/

GameFAQs: Final Fantasy VI (PSX)

Features user-submitted FAQs, guides, walkthroughs, codes, save files, and reviews as well as a messageboard.
http://www.gamefaqs.com/console/psx/data/23391.html

Final Fantasy VI Online

FAQs, guides, maps, music and downloads.
http://www.ffonline.com/ff6/