This one is pretty cool.....
Might be a bit laggy after you do the first block update and the sand starts to fall.
Dig through the first layer and the nether is below. I set the amount of air so the ghasts could spawn on the top layer as well.
Exploding floor w/o crashing the computer
That last one's pretty cool. In fact, when I tried it, a village spawned not far from me, and the testificates were stupidly walking all over the pressure plates, hurting themselves. Despite the water, there seemed to be a bit of building damage as well. The seed is -8533567695617183650, and you can find the village near X=-700, Z=500.
Also, here's another cool preset I made: 1;7,2x10,0,60x20;8 It's several layers of glass on top of lava, and it just looks cool when you "dig" through the glass.
This one is really cool. It was posted in the custom maps forum but I think it needs to be posted in this thread with all the other great presets: 1;7,56,1,49,14,73,15,49,16,4x1,32x24,5x12;2 http://www.minecraftforum.net/topic/1479183-"sans-serif"> The idea here is to trade with the villagers for a diamond pickaxe so you can mine past the obsidian to the good ore. You also have to go from town to town to find a sappling. Each world generates differently so posting cords will do no good. The first render I tried, I walked for what seemed like forever and no sapling. The second world I generated I found a sappling in the third village and while I was just making a First Impression for my site, wouldn't you know it, the first town I found had a sappling! "sans-serif">
Anyway, try this preset, it's so much fun. Oh, and don't start with a bonus chest as that defeats the whole purpose of the map.