Doom-related
DoomWorld - The definitive source for Doom news, information and development
NewDoom - Dedicated to the fans and community of id Software's DOOM games
ZDoom - Home of the ZDoom source port
Skulltag - Home of Skulltag, a multiplayer child port of ZDoom with GZDoom features
EDGE - Home of the Enhanced Doom Gaming Engine
Doomsday HQ - Home of the Doomsday Engine, jDoom, jHeretic and jHexen

DRD Team Archives
Paul's Canvas Workshop