Okay, this is one freaking long command, but it is very usefull. It spawns a single villager with the ability to give you a full stack of any spawn egg, as well as a monster spawner. Sounds great, but there is a heavy toll. You need a Dragon Egg for the spawn eggs, and a Nether Star for a spawner. Other than that, the eggs have relatively accesible ingredients, such as slime blocks or TNT.