I'm currently writing a pack of crack me's for Java, I have 6 levels finished but I'm planning on at least 20 before the release.
I'll also write a complete tutorial on reversing each crack me, it starts off easy and ends hard, so this will be a great teaching system.
If anyone has any suggestions for protection methods in Java, feel free to message me any time to talk about it, I'd love to add new methods of protection into it.