CraftBukkit Build 1.6.2-R1.0 [Tested]
This plugin disables xp from mobs spawned by xp farms. I've added auto update support so It will warn you If their is a new version. This has not been fully tested tho. Every entity, the mob in this case, is given a UUID which is a unique key for every mob that doesn't change. Basically this plugin creates a list of all the uuids, every time a mob spawns if it's from a spawned then it's uuid is added to the list. Every time the mob dies it is removed from the list and if its uuid is in the list then cancels the xp drop event thus meaning it does not drop xp :D
