ultimate iron ingot farm XD
http://www.youtube.com/watch?v=Sz5Ksb69MMA&feature=related
First I was iffy about villager eggs. Now I'm 100% against.
1ce, first off:
The player can add buildings to a NPC Village to cause more Villagers to spawn there. The requirements for a building are as follows:
Must have a door.
Must have a solid roof of any kind of solid block aside from blocks such as iron bars or glass panes(Tested on 1.2.5, works in over 20 different cases in a designated area)
Buildings may be constructed out of most kinds of blocks provided that they were placed there by the player.
Must have a 3X3 space inside to be counted as a house. I.e, the building itself must be 5X5 including walls.
To properly register each door as a house, a villager must be within a radius of 16 blocks horizontally and 3 to 4 blocks vertically of it. Houses may unregister as houses if there are no villagers within range for a period of time.
Each door successfully registered as a house counts as 35% of a villager, meaning that every 3 registered doors produces a villager and every 20 registered doors is an additional villager. 21 doors will make 8 villagers.
Second, look at the rates for trading.
http://i.imgur.com/0oitJ.png