This is the flat world I use for creative mode. It's extremely simple and clean. You can either use the preset key shown below or download the worldsave. The only real difference in the worldsave is that it contains a 2x2 column of Chiseled Sandstone to mark the center of the map.

Preset key:
3;minecraft:bedrock,9*minecraft:sandstone:2,244*minecraft:air,minecraft:glass;-1;

Features

• Endless superflat world. No borders.
  
• Desert blocks (easier to see redstone, and animals do not spawn in desert)
  
• Glass ceiling (keeps rain out but allows sunlight in)
  
• 244 blocks high of air (plenty of headroom)
  
• 10 blocks deep of ground (1 bedrock layer, 9 sandstone layers)
  
• Consists of only Air, Bedrock, Glass, and Smooth Sandstone blocks.
  

Additional Notes

• The Salt Flat photo is provided by Ronan Crowley at Flickr.com.
  
• The default texture pack is being used for all the screenshots.
  
• No rights reserved. Use this map however you like.