The Monsters Know What They're Doing     Dungeons And Dragons 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
Flee, Mortals     D&D 5e (no source link)
Ultimate Bestiary: Revenge Of The Horde     D&D 5e original/official source
Monster Monday (web)     D&D 5e original/official source
Monster Ecology Anthology     D&D 5e (no source link)
Dragon Magazine     D&D 2e/3e (no source link)
MojoBob (web)     D&D 2e original/official source
D&D 2e Monstrous Manual     D&D 2e original/official source
Scruffy Grognard's Monstrous Manual     D&D 2e (no source link)
AD&D Monster Manual     AD&D 1e (no source link)
Dragonlance Bestiary     SAGA (no source link)