Add yours, add categories, link everything!

Mapping, Gaming, Singleplayer, Design: http://www.celephais.net/board/

Modding, Coding: http://www.inside3d.com/

NetQuake: http://www.quakeone.com

QuakeWorld, Multiplayer: http://www.quakeworld.nu/

News aggregation: http://www.planetquake.gamespy.com/

Germany: http://www.quake.de/

Brasil: http://www.quakebrasil.com.br

Czech: http://www.quake.cz/ (Quakeworld and other Quake titles)

All console variables in DarkPlaces: http://www.quakewiki.net/darkplaces-wiki/console-variables/

Quakeguy (FifthElephant)'s tumblr: http://quakeguy.tumblr.com/

Resources for various games http://www.gamers.org/pub/

Crash: http://www.quake2.com/crash/reviewsplash.htm

Daz (Custom Gamer) on youtube:http://www.youtube.com/user/darrenweekes

Daz's Quake 1 reviews: http://www.youtube.com/playlist?list=PLB827907AD18E9966

[Kona]: Ratings: http://www.electricescape.com/etherealhell/index.php/ratings/ratings-quake-levels

[Kona]: Reviews (occasionally feat. Tronyn): http://www.electricescape.com/etherealhell/index.php/reviews/quake-reviews

TEAMShambler: https://www.quaddicted.com/webarchive/teamshambler.planetquake.gamespy.com/

Tronyn: https://www.quaddicted.com/tronyn-reviews/start

Underworldfan (occasionally feat. Tronyn): http://www.quakewiki.net/archives/underworld/

Bot setup tutorial by Johnny Law http://neogeographica.com/site/pages/guides/deathmatch_with_bots.html

Level design tutorials by Spirit http://maps.rcmd.org/tutorials/

Level design tutorials, centered around Quake 2 and 3 http://www.quake2.com/qworkshop/info/index.htm

Worldcraft/Hammer/J.a.c.k. mapping tutorial http://www.quake-1.com/wc16a-tutorial/

Mapping tutorial for Quake engine's games by Richard Neff http://panjoo.tastyspleen.net/rust/tutorials/beginner/beginner.html

Mapping tutorial in BSP for Quake engine's games http://www.bspquakeeditor.com/tutorials.php

Mapping tutorials and resources https://www.quakewiki.net/archives/worldcraft/index2.shtm

Mapping tooltips by aguirRe http://www.quaketastic.com/files/mapping_tooltips.txt

Texturing by Metlslime: http://www.celephais.net/stuff/texturefaq.htm

Coding/hacking/Quoth tutorials by Preach https://tomeofpreach.wordpress.com/

QuakeC AI tutorials https://www.quaddicted.om/webarchive/minion.planetquake.gamespy.com/tutorial/main.htm

Quake 2 mainly http://www.3dgamersedge.com/

Quake 2 MP only http://maps.clanwos.org/maponserver/

Quake 2 http://www.quake2.com/awoq2/

Quake 2 mainly, but also tons of Quake and HL. ««DEAD»» http://tenfourmaps.telefragged.com/php/main.php/

Quake 3 Arena http://lvlworld.com/

Doom http://www.doomworld.com/idgames/

Unreal http://unrealarchives.com/

Unreal http://www.unrealsp.org/legacy/

Unreal http://www.oldunreal.com/wiki/index.php?title=Maps

Half-Life, Half-Life 2 http://www.runthinkshootlive.com/

Sites that go by the name "Quake Wiki":

• This one is solely focussed on Quake 1. A bit lacking in content, but has some nice introductory information for those interested in the technical side of the game (e.g. beginner mappers and modders): https://quakewiki.org/

• This one has plenty of basic information (weapons, monsters, etc.) about Quake 1, Quake 2, Quake 3 Arena and Quake 4: [link removed]
  • Spirit says: It is full of inaccuracies and made-up things as well.
  • Icantthinkofanickname says: I've removed that link (I think I was the one who added it initially; it was a long time ago); for this and other reasons. Better to link to more legitimate and less shady sources.

• This one seems like a cross between a wiki and a Quaddicted-like repository of mods and maps: http://www.quakewiki.net/

* Doom wiki (which has plenty of information relevant to Quake as well): https://doomwiki.org