Creature Codex (web)     Pathfinder original/official source
The Monsters Know What They're Doing     Dungeons And Dragons original/official source
Angry Golem (web)     D&D 5e original/official source
Creature Chronicle (web)     Pathfinder original/official source
Monster Manual     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 3     D&D 4e original/official source
Dungeons And Dragons Essentials: Monster Vault     D&D 4e (no source link)
Dragon Magazine     D&D 2e/3e (no source link)
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)
The Monster Overhaul     OSR (no source link)
Baby Bestiary 2     Any original/official source