I was thinking that it would be cool if you could craft spawn eggs and spawners.
To craft a spawn egg, you'd have to put an item corresponding to a certain type of mob with 8 eggs surrounding it. (List of items corresponding to mobs below) Then, to make a spawner, put a spawn egg in a crafting table with 8 iron bars surrounding it!

Mob-Item list: (Those that I haven't decided on yet are listed with "???")
Passive mobs:
Pig: Raw Pork
Cow: Raw beef
Sheep: Wool (any color)
Chicken: Raw Chicken
Wolf: Bone
Villager: Emerald
Bat: ...dafaq would you want to spawn a bat??? (If for some crazy reason you want to, I guess you could use black wool?)
Squid: Ink sac (if you're sky, you'll never make a squid spawn egg, but...)
Horse: Leather
Ocelot: Fish

Hostile mobs:
Zombie: Rotten flesh
Skeleton: Arrow
Spider: Spider eye
Cave spider: Potion of poison (any power level/duration, minimal recommended to save resources)
Creeper: TNT
Zombie Pigman: Gold ingot
Ghast: Ghast tear (WARNING: Ghasts are EXTREMELY dangerous!)
Silverfish: Stone (Also, perhaps putting a silverfish spawn egg plus 8 stone/stone brick would make a stone/brick monster egg!)

Please comment if I've missed anything, or if you have an idea for what to do on the ???'s