Fragadelic
Total conversions and extra levels.

DooM TC Webring
A webring for total conversion projects.

Parallel Team
Various episodes including Parallel Dimension I and II, and Fragfest Initialised.

Opulent's Doom2 Page
A best WADs list, mostly for Doom 2 single player.

Doom Underground
Reviews and screenshots of add-on levels.

TeamTNT
Icarus, Eternal, TNT Evilution, several deathmatch packs, and other projects.

Doomer's Recess
Personal site with reviews and downloads. Also includes the megawad project "2002 A Doom Odyssey".

Paul's Doom Page
Personal site with some single levels and some larger projects.

The Doom Site
Small collection of WADs, some original. Also lists the author's favourite utilities.

Chris' Shockwaved Doom Page
Personal site with original add-on levels.

Transformers Doom Page
Graphics conversion.

Gatchaman Doom
Partial graphics conversion, with screenshots and download.

Holger & Bjorns Doom Stuff
Infinity, Serenity and Eternity, new episodes for Doom, and other new levels.

Visions Of Doom
Personal add-on reviews site.

Doom Legacy Wads
Collection of WADs which work with Legacy, with descriptions and downloads. Also technical information, screenshots and original artwork.

Team Kill
Add-on episode for Doom 1. Downloads, screenshots, music and progress information available.

Karthik 82
Personal site with reviews and new levels.

Geniacs Doom Wad Played List
One-line descriptions for a large number of add-on levels.

Doom Wad Station
Personal site with WADs. Also reviews of other levels and a collection of downloads.

Bird Nest Designs
32-level deathmatch WAD for ZDoom.

Erik Alm's Page of Doom
Personal site with new levels.

Sarge Baldy's Hardass Doom Reviews
Reviews, with ratings and screenshots.

JDoom Models
Models for JDoom port. [English/Polish]

Cyberdemon Army
New level pack for Zdoom. Includes screenshots, maps, and forums.

Brad Spencer: maps/demos
Personal site with original levels and demos, and links to the author's favourite add-ons.

GoldenEye Doom2
Total conversion with a Bond theme. Downloads, screenshots and information available.

DoomSearch.com
Searches the idgames archive.

Doom3 Stronghold
A fortress style gameplay mod for Doom 3. Gives news about progress and information about the team.

Doom 3 Mod Foundry
Discussion forums for open source projects for Doom 3.