Sources of the Complete Monster project

Pink Knight 42, Complete list of every creature in the Monster Manual, Volo's Guide to Monsters, Tome of Beasts and A Monster a Week Comenpdium (reddit) (gsheet) (backup)
Soz Surt, Copy of Complete Monster List for Adventures (gsheet) (backup)
Zenkall, Tome of Beasts (obsidian)
drow, 5e Monster List (donjon)
Monsters » Dungeons & Dragons — Donjons & Dragons — D&D 5, (aidedd)
BoLS Interactive L, The Hypertext 5e d20 System Reference Document™ (srd)
BoLS Interactive L, The Hypertext d20 SRD™: Pathfinder Reference Document (bestiary) (bestiary2) (bestiary3) (bestiary4) (bestiary5)
The Orr Group, LLC, Monsters List of the D&D 5th Edition Compendium (roll20)
Open Gaming Network, SRD v1.6.0 Creatures (d20pfsrd)
Ian Toltz, 4e Monsters (asmor.com)
Wizards of the Coast, Consolidated Lists: Monster Index (archive)
D&D Beyond, Monsters (dndbeyond)
Echohawk, Complete D&D Monster Index (xls)
Dave Arneson, Dungeonmaster's Index (amazon)