SITE AND FORUM
Official MoOIII Site - At Quicksilver Software Inc.
IGMoo forum

The Orion Sector - A comprehensive site with official MoO FAQ
OSMoo forum

Apolyton - Apolyton's MoO 3 section
Moo3 forum

Mods
Moo3Mods.com - Your central mod vault

GAME PLAY INFO
CoW - an Anti-Structural Master of Orion 3 Guide/Encyclopedia

Lore_Weaver Strategy Guide - An eight part strategy guide each covering one specie and its race hosted at the IGMoo forum. Note: Pre-release data.

TUTORIAL
Custom Player Flags - An example of how to created player flags for MOO3 at Quicksilver

Another Flag Guide - At The Orion Sector. See also Player Examples and comments.