This seed was discovered by Aminom and is a large flat plain surrounded by unusual features. Rather than having one area of interesting terrain, this seed has several, including two sizeable floating islands at (x=337, z=-307).
The main feature of this seed is a tall arch adjacent to a large floating island. The rest of the terrain is very mountainous with dense woodland. (Note: the seed is Invinsible not the correct spelling of Invincible).
This seed contains many dramatic overhangs and huge floating islands all very close to spawn. As you can see from the first and second screenshots an open lava pool causes a forest fire when you initially start the map however it quickly burns out.
This seed, shared by Minecraft forum user IntrepidOtter, contains floating islands, massive arches, cliffs and many other interesting features. The features are distributed over a very wide area so you will certainly not run out of places to explore!
If you feel like a challenge use the seed gargamel. The spawn area is inside a pitch black cavern with only a very thin exit. If you manage to get out you will find yourself surrounded by steep mountains and dark pits filled with dangerous mobs.