Build engine Discord: https://discord.gg/XR6eH9W

Duke3D SDA threads:
https://forum.speeddemosarchive.com/post/duke_nukem_3d_megaton_edition.html
https://forum.speeddemosarchive.com/post/duke_nukem_3d_speedrun.html

Some of the information in the "Game Mechanics and Glitches" page is based on prior work from Joe Lennox's website, Red-Stars.net, which has a good write-up of a lot of the Duke speedrunning tricks, and also some per level speedrunning notes:
http://www.red-stars.net/content/Duke_Nukem_3D/

The Wikia Duke Nukem wiki contains quite a bit of useful info:
http://dukenukem.wikia.com/wiki/Duke_Nukem_3D

Duke R.T.C.M (Resources for Total Conversions and Modifications) was a well-maintained website full of info, documentation, and downloads for pretty much all of the Build Engine games. (files mirrored on dukeworld)
http://dukeworld.com/2001-current/rtcm/redneck-faqs/
original address https://web.archive.org/web/20160111131109/http://dukertcm.com/
http://www.r-t-c-m.com/
LLCoolDave's version of the Duke3D Done Quick project (circa Dec. 30, 2004) (distinct from the earlier Kineox version)
JFDuke3D .dmos of the runs are available on the archive:
https://web.archive.org/web/20041230163614/http://www.metroid2002.com/llcooldave/duke3D/recordlist.htm

Fernito's Glitch City map, a challenge map with a focus on Duke glitches:
http://www.red-stars.net/games/duke3d/GLITCH.MAP
http://www.youtube.com/watch?v=rJ1UQ0elpYY

You can find the source code for Duke Nukem 3D Megaton Edition here:
https://github.com/TermiT/duke3d-megaton

The Chocolate Duke source and dissection notes can also be useful:
http://fabiensanglard.net/duke3d/index.php

You can find video of the XBOX 360 Duke3D speedrun leaderboard demos here (Huge thanks to King Mamba 48 for recording and uploading these!):
Any%: http://www.youtube.com/watch?v=QxraCgpbkiM
100s: http://www.youtube.com/watch?v=o5s01R4xQyc

Also, if you haven't seen it already, you should definitely watch LLCoolDave's most recent AGDQ2014 run of Duke Nukem 3D: Megaton Edition (which includes a glitch exhibition):
http://www.youtube.com/watch?v=RxdUFOKG3r4

Redneck Rampage -specific

http://www.r-t-c-m.com/
Look for the Redneck Rampage section under "build games". All info has been copied over.