RTC-3057 - 7 futuristic levels for ZDoom. - http://www.nautrup.com/3057/
I ate them... - Personal site with information on, and links to, projects the author has worked on. - http://thefish.8m.com/
DarkWolf's Doom Page - Personal site with new levels, ongoing projects and a script archive. - http://darkwolf.slipgate.org/
Fredrik Johansson's Website - Personal site with levels (including the Vrack series), textures, and miscellaneous resources. - http://fredrik.mancubus.net
Co-Op Tested Doom II Maps - Brief reviews of add-ons in cooperative mode. - http://wondersmith.com/coop/doom2.htm
Nostromo's Place - The official HACX page. Also information and downloads for Strain and other projects the author was involved with. - http://www.drnostromo.com/hacx/
Doom II Deathmatch - The "Trio" series of deathmatch levels. - http://www.pcug.org.au/~dean/
St John's Doom - Level modelled on St John's College, Oxford. - http://www-cs-students.stanford.edu/~stong/sjcdoom/sjcdoom.html
Dr. Iguana's Doom II Stuff - Original deathmatch levels. Also editing and play tips. - http://www.chembio.uoguelph.ca/driguana/doom2.htm
WolfenDoom - Wolfenstein 3D meets Doom in this total conversion. - http://www.doomworld.com/wolfendoom/
Send Coffee - Four levels that work on single player but primarily for deathmatches. - http://www.sendcoffee.com/minorsage/sctoys.html
Alien Vendetta - A hard 32-level megawad. - http://www.doom2.net/~av/
Mordeth - A full four episodes set in medieval times. - http://mordeth.doomworld.com/
The Darkening - Contains single player and deathmatch wads with a new storyline. - http://www.doomworld.com/darkening/
Securitron - Stop the self-aware "controlling system" in 2076. - http://doomworld.com/securitron/
Twice Risen - Unfinished total conversion, only a preview download is available. - http://www.doomworld.com/twicerisen/tr.shtml