I know heads are worth a lot of diamonds but I think some heads will become worth less soon as in snapshot the latest snapshot for 1.8, mojang announced that you will be able to get creeper, skeleton and zombie heads in survival. Assuming that it is a lucky drop from mobs, will creeper and skeleton heads (as zombie spawners are disabled I think) be worth less? I will put a link to snapshot 14w30b.

EDIT: I have found out that it's a lucky drop but only when a charged creeper kills a creeper, zombie or skeleton meaning that, as I think lightning is disabled, it will still be hard to obtain heads.