Concurrent Programming in Java: Design Principles and Patterns
Excellent Java threads tutorial book from The Java Series by Doug Lea (Addison-Wesley). Covers programming with Java threads in detail, shows the reader how to think about concurrent programming. Cookbook of design patterns for concurrent programming instructive and useful for new and experienced threads programmers.
http://gee.cs.oswego.edu/dl/cpj/

Jurtle
A simple programming environment combined with a Java tutorial for learning to program in Java and teaching programming in Java. [Commercial]
http://www.otherwise.com/

Seminar: Concurrent Programming in Java
A course covering all aspects of multi-thread programming in Java from plain synchronization over Java 5.0 concurrency utilities to memory model issues.
http://www.angelikalanger.com/Courses/ConcurrentJava.htm

ACM Crossroads: The Use of Java as an Introductory Programming Language
How GA Tech moved to teaching Java at the introductory programming level; ACM Crossroads
http://www.acm.org/crossroads/xrds4-4/introjava.html

Java Thread Programming
Java Thread Programming - a comprehensive, 510-page book by Paul Hyde. It teaches readers how to effectively and *safely* build multithreaded applications.
http://www.programix.com/threadbook/

The Advanced Java/J2EE Tutorial
Learn more about JavaBeans, JDO, Visual Programming, Component Model, Design-Time Interface, BeanInfo, additional BeanInfo, Bean Instantiation, Persistence, BoundProperty, Constrained Property
http://my.execpc.com/~gopalan/java/java_tutorial.html

Groovy Java Genetic Programming
Genetic Programming (JGProg) is an open-source pure Java implementation of a strongly-typed Genetic Programming experimentation platform.
http://jgprog.sourceforge.net/

Lea, Doug
Author of Concurrent Programming in Java: Design Principles And Patterns. A collection of resources to Java, Object Oriented Programming and Design Patterns. Also, Lea's Java concurrency library is available here, as Public Domain.
http://gee.cs.oswego.edu/dl/

Interactive Programming In Java: A Community of Interacting Entities
Word game examples of Java programming. Includes Pig Latin and Ubby Dubby.
http://www.cs101.org/ipij/interlude-stringXformers.html

Introduction to Programming Using Java
A free Java programming textbook by David J. Eck, available for use on-line and for downloading.
http://math.hws.edu/javanotes/