Doom Beastiary
From DoomWiki.org
Doom Beastiary (sic) is a website created and hosted by Nick "NiGHTMARE" Baker. It contains general information about Doom monsters (name, health, speed and attacks), but also features numerous fan-created monster ideas (each represented by a single sprite, and sometimes proposed in-game statistics).
The site is inactive, having not been updated since December of 2003. Daniel "Tormentor667" Gimmer created his Realm667 Doom Beastiary in 2007 as a monster resource site and an homage to Nick Baker's Beastiary.
Some of the monster concepts have been turned into fully developed custom monsters in the ZDoom Monster Resource WAD.