I figured this would be a great idea as even i personally would like to know what monsters drop which items. So i will make a start, as the first player on the server i have killed a few things although i have only received little drops.
This topic will be ongoing and will be heavily updated during time.
Giant Rats (Level-3) - Drops: Bronze, Iron, Mithril, Some Adamant armour.
Phoenix (Level-666) - Drops: Pimpz Chestplate, Green Chestplate, Black Chestplate. (Custom Bandos Chestplates)
Flambeed (Level-149) - Drops: Pretzels.