Iron golems are an incredibly useful mob, mostly due to their use in Minecraft iron farms. But their ability to attack hostile mobs, as well as aggro slimes, make them nearly essential to late-game ...

Minecraft Tutorial - How to Create a Mob Trap and Item Collection Machine by drunkoncustard. Note that to speed up the process, this machine was created in Minecraft's Infdev mode.

Flying machines are interesting Minecraft redstone contraptions. They utilize the ability of slime and honey blocks to stick to other blocks to pull a piston contraption along as it pushes itself.