CaveWorlds is a Bukkit/Minecraft world generator that creates funny worlds with huge cave system around y=100 till y=150
Some code is from variety of tutorials some from Youtube some from bukkit forums and some from other forums. Here are some tutorials used and watched: http://forums.bukkit.org/threads/basic-creating-custom-world-generators.24569/#post-678581 http://forums.bukkit.org/threads/basic-creating-custom-world-generators-new-api.79066/
If you find code form your tutorial not mentioned here send an email or make an issue or contact in what ever way you want.