Must have Code Quality Plugins for Eclipse

Findbugs looks for bugs in Java programs
Update-Site: http://findbugs.cs.umd.edu/eclipse/

PMD scans Java source code and looks for potential problems
Update-Site: http://pmd.sourceforge.net/eclipse

Checkstyle helps you ensure that your Java code adheres to a set of coding standards
Update-Site: http://eclipse-cs.sourceforge.net/update/

Code Analysis Plugin (CAP) checks dependencies between the classes and packages and gives you a hint about the architecture, reusability and maintainability.
Update-Site: http://cap.xore.de/update

moreUnit is a eclipse plugin that should assist you writing more unit test.
Update-Site: http://moreunit.sourceforge.net/org.moreunit.updatesite/

EclEmma is a free Java code coverage tool for Eclipse.
Update-Site: http://update.eclemma.org/

JAutodoc is an Plugin for automatic adding Javadoc and file headers to your source code.
Update-Site: http://jautodoc.sourceforge.net/update/

A quote from Rick Cook

Programming today is a race between software engineers striving to build bigger and better idiot-proof programs, and the universe trying to build bigger and better idiots. So far, the universe is winning.

Rick Cook, The Wizardry Compiled