1.7: schönster

(This seed is for Minecraft 1.7 and earlier.)

Clay. That's what I first found. And that's what you want, right? However, this Minecraft seed has much much more. It has the biggest cave ever. And by big I really mean B-I-G!

The coordinates of the above picture are these:
x: 10
y: 15
z: 220

Here's more coordinates:

1.7: -1784338777788894343

(This seed is for Minecraft 1.7 and earlier.)

A Minecraft world created with the seed -1784338777788894343 defies the laws of Physics with countless mountains and other fancy structures. Below are screenshots taken near the spawn point. Let them tell more than thousands of words.