Open Source Projects at JavaKB - An extensive directory of Java open source projects. - http://www.javakb.com/Uwe/DirCat.aspx/Dir/Software
Manageability - Java Open Source Lists - A Collection of Collections of interesting Open Source projects written in Java. - http://www.manageability.org/blog/opensource/view
Java Source Codes @ VyomWorld.com - Categorized Java source codes from beginners to advanced level topics. - http://www.vyomworld.com/source/LanguageHome.asp?LangId=5
PLEAC-Java - A reference to solve common programming problems using Java. [Open Source] - http://pleac.sourceforge.net/pleac_java/
cgi-bin.com: Java - Provides annotated, user-reviewed links to a wide variety of free and commercial Java applets, servlets, and JSP. - http://www.cgi-bin.com/Java/
Servlet and Java ServerPages Source Code Archive - Source code archive from Sun Microsystems Press book, "Core Servlets and Java ServerPages". All code free for unrestricted use. - http://archive.coreservlets.com/
Freshmeat.net Java projects - Browse all Freshmeat.net Java projects (mostly free software) and filter them by various categories. - http://freshmeat.net/browse/198/?topic_id=198
Free Software Foundation Java Pages - A collection of Java programs and projects that are licensed with the Gnu Public License (GPL). [Open Source] - http://www.gnu.org/software/java/java.html
Java Source - GUI and console applications with sources. Download source code or submit source code. - http://www.javasource.150m.com/
Giant Java Tree: GJT - Experiment in Java open source developer support: provides developers with a free, publicly accessible, browsable CVS repository, automated online JavaDoc support, an automated release and distribution system. 2000+ classes in 200+ packages, including: jE - http://www.gjt.org/