I thought it would be fantastic for a modder to create a mod for capturing various mobs for transportation purposes, rather than just killing them.
To craft the trap, use 6 wood planks, 2 steel bars, and a piece of meat in the middle.
After setting the trap down on the ground, the player right-clicks it to activate it. Any mob within 16 blocks of it is attracted to it. Once the mob comes into contact with the trap, it springs close with the mob trapped inside. The trap drops to the ground and the player can then pick it up. The next time the player uses the trap, it opens and the mob comes out. Could be thrown like an egg, and be destroyed so the player has to build another to trap again. If the creator wants to avoid using new graphics, the mob spawner could possibly work as a graphic.
I am suggesting this because I am building a zoo of all the mobs, and it's difficult to lure the aggressive mobs to their new homes without killing them or being killed.
This type of thing would be useful if compatible with other mods that add new mobs as well, such as Mo' Creatures and the like.