In Nomine (official page):The official page, with detailed descriptions of all the books (including artwork and excerpts), errata, FAQs, and news.
In Nomine Collection:The best of the In Nomine mailing list: plot hooks, adventures, NPCs, theories, and tips.
A Most Foolish In Nomine Web Site!: Manny Nepomuceno's In Nomine site, containing sundry game resources for In Nomine. Also includes writeups for In Nomine Dragonlance and In Nomine Philippines.
Amadán's In Nomine Page: Several thought-provoking NPCs, as well as In Nomine New York and San Francisco (see Settings), In Nomine Touched by an Angel, and some cuts from the Corporeal Players Guide
Annotations: In Nomine: New Superiors (including Heretical ones), NPCs, fan fiction and the odd location or two
Liber Licentiae Moeticae: Seriously oddball and weird; mostly NPCs, with some fun artifacts, minor choirs and bands, the occasional fan fiction and adventure seed. Warning: may make your brain hurt.
Morning Star Ascendant: Golem rules, new NPCs, choirs, superiors, plot seeds
Nobody Expects the Divine Inquisition: NPCs, gadgets, intriguing new Discords, and house rules.
The In Nomine Cookbook: A searchable compendium of powers available to Celestials in In Nomine. Incomplete; currently limited to Angelic powers and some common Songs.
The Last Days: A not-quite-canonical view of In Nomine. It contains new or modified Superiors (e.g. Uriel or Khalid), NPCs, adventure seeds, and rules for adapting In Nomine to a LARP environment or playing Word-bound Celestials. Some overlap with the In Nomine Collection.
WebRing: innomine: List of interlinked sites forming the "In Nomine RPG Webring".