Creature Codex (web)     Pathfinder original/official source
The Monsters Know What They're Doing     Dungeons And Dragons original/official source
Creature Chronicle (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     D&D 4e (no source link)
Monster Manual 2     D&D 4e (no source link)
Monster Manual 3     D&D 4e (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)
Hacklopedia Of Beasts Vol 7     Hackmaster original/official source