Dracopedia Bestiary: An Artist's Guide     Any 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
Pathfinder 1e Bestiary 1     Pathfinder original/official source
Pathfinder 2e Bestiary 1     Pathfinder original/official source
Tome Of Horrors Complete     Pathfinder original/official source
Mythic Monster Manual v1     Pathfinder original/official source
Mystery Monsters Revisited     Pathfinder original/official source
All Sorts Of Critters (web)     Pathfinder original/official source
Monster Manual     D&D 5e original/official source
Monster Monday (web)     D&D 5e original/official source
Monster Ecology Anthology     D&D 5e (no source link)
Monster Manual 3     D&D 4e (no source link)
Scruffy Grognard's Monstrous Manual     D&D 2e (no source link)
Hacklopedia Of Beasts     Hackmaster original/official source
Fantasy Age Bestiary     Fantasy Age original/official source