Eclipse
Eclipse plugins, Eclipse Project, Eclipse Project Wiki Wiki Web, Eclipse Tracker, Eclipse-Workbench, Essential Eclipse - The Visual Tutorial, eva/3 Application Builder, Fat Jar Plug-In, Fatborn - Eclipse Plugins, Findbugs Plug-in for Eclipse
Amy
Cross-platform, multi-language IDE with syntax highlighting, code completion, and automatic Makefile generation. [Open Source, GPL]
Ginipad
Integrated Development Environment for Java, written in Java itself. It provides syntax highlight, automatic code completition, edit-compile-execute cycle. It require JDK 1.4. [Open source]
Gwydion Sheets
Gwydion Project's hypercode programming environment for Java supports complex hypertext interlinking, multiple groupings of code, and searching of code and documentation fragments. [Open Source, Public Domain]
jEdit
Programmer's text editor; includes support for dynamic download and installation of new plugins from a central plug in server. Java, XML and JSP source are well supported.
NetBeans
Fully-featured Java IDE written completely in Java, with many modules available, such as: debugger, form editor, object browser, CVS, emacs integration, scripting support, make, Ant, and unit testing. [Open Source, MPL-like]
Red Hat Source-Navigator
A source code analysis tool. With it, you can edit your source code, display relationships between classes and functions and members, and display call trees. [Open Source]
Sun Labs Jackpot
Source code metrics framework plugin for NetBeans.