For now, zombies drop diamonds, from 1 to 64. They also drop Iron Ingots, Gold Ingots, and Emeralds.

Everything else besides diamonds drops by 1. (1 Iron Ingot, 1 Emerald, 1 Gold Ingot)

Zombies are also guaranteed to have armor on, and have a higher chance to spawn with a weapon.

Zombies won't always drop their weapon or armor.

There is also a small Easter egg with the farmer villager... maybe you can find it?

As you can see, only by killing a couple of zombies, I already have stacks of diamonds, golden armor (for nether or protection) an enchanted iron sword, and a couple of emeralds, gold, and iron ingots.

Randomly spawning zombies, all wearing armor of some sort. It's also easier to get chain now, as you can see. One zombie even has an enchanted helmet!

I didn't kill them by hand, but instead used the /kill command. You can still see, though, that they still dropped diamonds.

What could you use this for?

Maybe you wanted a new survival for a change. Something easy or unexpected. Maybe you wanted to troll your friends?

Another good use for this is some sort of dungeon crawler. Better weapons can be bought with higher prices of diamonds, gold, iron, or emeralds. Diamonds are the "main currency".