Doom Legacy Wads - Collection of WADs which work with Legacy, with descriptions and downloads. Also technical information, screenshots and original artwork. - http://dlw.doomwadstation.com/
Doom Underground - Reviews and screenshots of add-on levels. - http://games.moria.org.uk/doom/du/
JDoom Models - Models for JDoom port. [English/Polish] - http://morgurth.dmkhost.net/
Doom Wad Station - Personal site with WADs. Also reviews of other levels and a collection of downloads. - http://www.doomwadstation.com/
ZDaemon - Multiplayer client / server port. Contains beginner's guides, strategy guide, FAQ, forums and a game launcher. - http://www.zdaemon.org/
GoldenEye Doom2 - Total conversion with a Bond theme. Downloads, screenshots and information available. - http://goldeneye.newdoom.com/index2.shtml