The Monsters Know What They're Doing     Dungeons And Dragons original/official source
Angry Golem (web)     D&D 5e original/official source
Atlas Animalia     Any original/official source
OSE Encounter Activity Tables     Any original/official source
Pathfinder 1e Bestiary 1     Pathfinder original/official source
Monster Codex     Pathfinder original/official source
Classic Monsters Revisited     Pathfinder original/official source
Monster Manual     D&D 5e original/official source
Monster Manual Expanded v1     D&D 5e original/official source
Monster Manual Expanded v2     D&D 5e original/official source
Flee, Mortals     D&D 5e (no source link)
Volo's Guide To Monsters     D&D 5e original/official source
Critter Compendium     D&D 5e original/official source
Monster Ecology Anthology     D&D 5e (no source link)
Monster Manual     D&D 4e (no source link)
Monster Manual 2     D&D 4e (no source link)
Dungeons And Dragons Essentials: Monster Vault     D&D 4e (no source link)
Dragon Magazine Monster Ecologies     D&D 2e/3e (no source link)
Monsters Compendium     Heroes Of Adventure (no source link)
Mystara Adversary Compendium I     Dragon Age original/official source
Baby Bestiary 2     Any original/official source