How do I create an empty minecraft world?

Solution 1:

With bukkit there are plugins that change the world generation to make the world flat, for example:

http://forums.bukkit.org/threads/wgen-flatlands-v0-1-makes-a-flat-world-860.20888/

http://forums.bukkit.org/threads/wgen-hugetractsofland-0-1-generate-a-flat-world-using-any-block-1060.28662/

You can also search http://dev.bukkit.org/bukkit-plugins/?category=world-generators for different types of world generators.

Note: I have not tried either of them.

Solution 2:

I would have to say that you just go into the server.properties file and edit it to be super-flat instead of default. The drawback to that is that you will not be able to go underground since it is only 3 blocks away from the 1 layer of bedrock.