Official websites important to you
J-Reborn.com – JAPANESE. Updates on the official releases for manga volumes, anime DVDs, video games, and card games.
Reborn Goods.com – Official anime merchandise of all kinds.
REBORN! on Crunchyroll is the legal way to get the series on streaming. However note that it’s REGION-RESTRICTED to USA, Canada, Australia, and New Zealand. The most recent episode is available with subtitles soon after airing in Japan. Uses Viz translations (“deathperation shot” and similar Americanizations).
Reborn! at Wikipedia — Comprehensive, and maintained by veterans. Use all the links.
KHR Wikia / Reborn Wiki — Also comprehensive, updated for more recent information.
Vongola.org — Everything else that is not covered by the Wikipedia entries, are here. Also includes links and fanlistings.
Over at MangaHelpers, Kirimi has kindly typed out more detailed information and more links (including less-than-legal options, if you’re interested). You will also find high-level forum discussions here about the manga.
Reborn Database — JAPANESE, collects relevant 2ch threads.
Vonola Manor — ITALIAN general info and update site.
Arcobaleno — GERMAN general info and update site.
Vongola Family — POLISH forum
General forums and communities
Fanlistings specific to characters are placed in their pages.