- Hey Arnold! at Nick-Asia.com - An Official Hey Arnold! page on the official site of Nickelodeon Asia complete with character bios, downloads and games.
- Hey Arnold! at the Internet Movie Database
- Hey Arnold! at TV.com
- Hey Arnold! at the Big Cartoon DataBase
- Hey Arnold! at Wikipedia
- Don Grande's Hey Arnold! Character & Episode Guide
- Arnold's Room at Multiply
- Hey Arnold! section at FanfictionNet — A site that hosts fan fiction of all sorts — this is a site where you can submit your own fanfics.
- Hey Arnold! at DevianART
- Arnold's Eyes, with episodes available for download
- Hey Arnold! episodes: Viewable online
- Hey Arnold! community at Livejournal
- Hey Arnold! fanfiction community on Livejournal
- Hey Arnold! Prompts community on Livejournal
- Hey Arnold! Rewatch community on Livejournal
- Hey Arnold! - The Jungle Movie Fanmade Projects! community on Livejournal - Community in which you can also share your ideas, plot devices for The Jungle Movie fan project, and also a place to post/share all of your projects, whether they be for The Jungle Movie, the years after The Jungle Movie, The Patakis, and even the years after The Patakis.
- Hillwood Times community on Livejournal
- Hillwood Guild community on Livejournal - "community is for super-secret Hey Arnold projects"
- Hey Arnold! - A Critical Analysis, by Tendra
- Hay Arnold 6th Season Project, started by Tendra
- Nadine's Hey Arnold Place
- Arnold's Neighborhood
- The Hey Arnold Forum on Yuku (formerly on Ezboard)
- Nick.com Message Boards
- Hey! "Arnold Stuff" — This site is loaded with "insider" material such as photos of cast members at the new Nicktoons studio opening party and drawings from some of the animators.
- The Unofficial Hey Arnold! Site © 1997-2006 Kim Burk, with information about the episodes, the cast, music, video etc.
- Cadpig's Shrine to Curly
- John’s Hey Arnold! Site (Jul. 2000)
- Arnold4Ever’s Page Of Virtual Wackyness (Aug. 2000)
- Helga’s Little Pink Book (Nov. 2000)
- The Patakis (Oct. 2002)
- An MDT Tribute To Helga G. Pataki (Nov. 2002)
- Rhonda’s Place (Feb. 2003)
- http://www.facebook.com/groups/320049038059044/ Hey Arnold TJM group
- Dé nederlandse fansite van Hey Arnold! — Forum hosted by Annemiek (English and Dutch)
- HEY arnold at Hyves.nl — Hey Arnold! community in a Dutch social network
- Heyarnold.Twotoasts.de — Bilingual English-German site with much downloadable stuf, articles, and very good episode synopses.
- Helgas Welt — German site
- heyarnold.prv.pl — Polish fan site
- Дневник Хельги — Fan forum including role playing games and fanfics.
- Hey, Arnold@дневники — Hey Arnold fans at Diary.Ru.
- Hey-Arnold.my1.ru — Forum
- hey-arnold.ru — information about the series
- Любители Мультика «Эй, Арнольд!» VKontakte — Hey Arnold fans in VKontakte social network
- Hey Arnold! forum on Nickelodeon-TV.ru
- Hey Arnold! forum on Nicktoons@6bb
- Сообщество Hey Arnold в LiveInternet
- Эй, Арнольд! на фан-сайте «Что с Энди?»
- Эй, Арнольд! Фан-сайт
- Эй, Арнольд! / Hey Arnold! группа во ВКонтакте
- El Diario de Helga Pataky — Spanish forum
- The Megawacky Dimension or  or  — Webarchive of the first bilingual English-Spanish Hey Arnold! site.
- Seriesnick: Series de Nickelodeon online — Watch the episodes in Spanish on-line.
- Sunset Arms: Un blog de HA!, by Graudlugh
Staff members' sites
- Maggie Groening: Twitter