The best one I know of is All-U-Want. It's so far only for 1.8, which is a shame, but it is incredibly useful for making virtually everything you could possibly want for a custom map. Custom splash potions, lore editor and name changer, supports the § character for color changes, custom enchants up to the maximum, (well over 20,000 levels of an enchantment!) and an entity spawner that allows you to customize literally everything you could ever need to customize. What mobs are riding, their health, enchantments on gear and custom gear for that matter, the ability to save custom EVERYTHING (Got one specific spawner setup you want to place several of? Save it as a template! Got a gear you want multiple of? Save it as an item favorite!) and all sorts of other features.
Thank you so very much! That sounds absolutely wonderful.
It's for 1.7 so I can either wait for 1.8 or try to make spawners in a 1.7 world and paste them into a 1.8 world. I don't know how well that will work but it's worth a try.
Thank you again!
EDIT: It runs out of memory every time I try to use it. Oh well. I can wait for 1.8 version; I'm waiting on a bunch of other mods anyway.