Tome Of Horrors Complete     Pathfinder original/official source
Fifth Edition Foes     D&D 5e original/official source
Volo's Guide To Monsters     D&D 5e 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 Fiend Folio     AD&D 1e (no source link)