Free Java IDE

NetBeans IDE 7.4
NetBeans IDE 7.4 extends the advanced HTML5 development support introduced in NetBeans IDE 7.3 to Java EE and PHP application development, while offering new support for hybrid HTML5 application development on the Android and iOS platforms. In addition, this release provides support for working with preview versions of JDK 8, and includes continued enhancements to JavaFX, C/C++ and more. Available in multiple language.

AIDE - Android IDE - Java, C++
AIDE is an integrated development environment (IDE) for developing real Android Apps directly on Android devices.

IntelliJ IDEA Community Edition
Open source version of IntelliJ IDEA, a premier IDE for Java, Groovy and other programming languages. Google Android development including latest SDK support

Eclipse is an open-source development platform that can function as a Java IDE.

DrJava is a lightweight development environment for writing Java programs. It is designed primarily for students, providing an intuitive interface and the ability to interactively evaluate Java code. It also includes powerful features for more advanced users. DrJava is available for free under the DrJava Open Source License, and it is under active development by the JavaPLT group at Rice University.

The tIDE java IDE
tIDE is a full featured opensource Java integrated development environment (IDE), distributed under the GNU General Public Licence (GPL).

BlueJ is a Java IDE and teaching environment.

A Free Java editor package written in Java.

Free Java v1.0
Free Java is an integrated development environment designed to help beginners write Java programs. It includes syntax highlighting and requires JDK 1.3 or higher.

A free ide written in Java with syntax highlighting and project management. It does not appear to have been updated in a long time however.