I took a seed from WubblesMinecraft (Youtube) and created a survival world out of it. My sister and I take turns, and we each built a house atop the sky isle. It's not much, but the sheer amazingness of the seed makes it something I have to share. I have many more awesome seeds, so just ask if you want any (you can give specifications on what type of seed too).

Note: I play 1.5.2, so I don't know if the seed works past there, but the world will function normally.

The coordinates for the Sky Isle are X 297, Z -434. The mini Sky Island is at X -139, Z -578, and the overhangs are at X 243, Z 236.