Angry Golem (web)     D&D 5e original/official source
Pathfinder 1e Bestiary 3     Pathfinder original/official source
Pathfinder 2e Bestiary 3     Pathfinder original/official source
Mythic Monster Manual v2     Pathfinder original/official source
Forgotten Foes     Pathfinder original/official source
Monster Manual Expanded v3     D&D 5e original/official source
Asian Monsters     D&D 5e original/official source
Monster Hunter Monster Manual     D&D 5e (no source link)
Scruffy Grognard's Monstrous Manual     D&D 2e (no source link)
AD&D Monster Manual     AD&D 1e (no source link)
The Monster Overhaul     OSR (no source link)
Baby Bestiary 1     Any original/official source