Charm Common Drop Monster :
Gold: Ice giant, Ice warrior, Ice spider, Fire giant, Rock crab, White wolf, Infernal Mages, Dagannoth, Black demon, Giant bats, Red dragon, Jogre, Ogre, Aberrant Spectre, Green dragon, Mutated bloodveld, Black knights, Jellies, Hellhound.
Green Mithril Dragon(4), Red dragon, Bloodvelds, Jellies, Poison Spiders, Wild Dogs, Iron(2)/Steel(3) Dragons, Wolf, Nechryael, Hellhounds, Green Dragon, Black knights, Aberrant Spectre
Crimson: Nechryael, Abyssal demon, White wolf, Dust devils, Greater demon, Metal dragons, Red dragon, Gargoyle, Bloodveld, Wolf, Shadow warriors, Waterfiend, Green Dragon, Black knights, Black demon, Aberrant Spectre, Cockroach soldier
Blue All monsters that drop charms drop blue charms at varying rates, so the best monster to kill for blue charms is a monster that you can kill fast, or one that drops multiple charms. This would include: Ice warriors, Fire giants, Dust devils, Gargoyles, Aberrant Spectres.
Abyssal: Monsters found in The Abyss (this does include abyssal demons).
Obsidian: Tzhaar Xil, Tzhaar Ket(2)
All charms: Fire Giants, Basilisks, Bloodvelds, All Dragons, Ogres, Jogres, Ice giants, Giant Rock Crabs, Hellhounds, Shadow warrior, Ice warrior, Dagannoths, King Black Dragon (4), bloodworm, Cockatrice