Below are some of my original World Files free for the taking.
They can be loaded into 'Mojoworld' or the free 'Mojoworld Viewer' available from Pandromeda or Mojoworld SE freely available with 3DWorld Magazine issue #66 (July 2005) you can then freely explore these real planet sized worlds and render your own scenes.
If you publish your renders,a credit on or alongside the image for creating the planet would be most appreciated.
You are welcome to use them for personal non-commercial use.
Please Note these are the only ones I currently wish to make public domain - check back for updates.

Thank You and Enjoy