Similar to PMD 
Open Source 
  Checkstyle  - Very detailed, supports both Maven and Ant.
Uses ANTLR.DoctorJ  - Uses JavaCC.  Checks Javadoc, syntax and calculates metrics.ESC/Java  -
Finds null dereference errors, array bounds errors, type cast errors, and race conditions.
Uses Java Modeling Language annotations.FindBugs  - works on bytecode, uses BCEL.  Source code uses
templates, nifty stuff!SpotBugs  - SpotBugs is the spiritual successor of FindBugs, carrying on from the point where it left off with support of its community.Hammurapi  -
Uses ANTLR, excellent documentation, lots of rulesJamit  - bytecode analyzer, nice graphsJCSC  - Does a variety of coding standard checks, uses JavaCC and
the GNU Regexp package.Jikes  - More than a compiler; now it reports code warnings tooJLint  - Written in C++.  Uses data flow analysis and a lock graph to
do lots of synchronization checks.  Operates on class files, not source code.JPathFinder  - A verification VM written by NASA;
supports a subset of the Java packagesJWiz  - Research project, checks some neat stuff, like if
you create a Button without adding an ActionListener to it.  Neat. 
Commercial 
  AppPerfect  - 750 rules,
produces PDF/Excel reports, supports auto-fixing problemsAssent  -
The usual stuff, seems pretty complete.Aubjex  -
Rules aren’t listed online.  Appears to have some code modification stuff, which would be cool to have in PMD. $299.AzoJavaChecker  - Rules aren’t listed online so it’s
hard to tell what they have.  Not sure how much it costs since I don’t know German.CodePro AnalytiX  -
Eclipse plug-in, extensive audit rules, JUnit test generation/editing, code coverage and analysisEnerjy Java Code Analyser  - 200 rules,
lots of IDE pluginsFlaw Detector  - In beta, does control/data flow analysis
to detect NullPointerExceptionsJStyle  - $995, nice folks, lots of metrics and rulesJTest  - Very nice with tons of features,
but also very expensive and requires a running X server (or Xvfb) to run on
Linux.  They charge $500 to move a license from one machine to another.Lint4J  - Lock graph, DFA, and type analysis, many EJB checksSolidSDD  - Code
duplication detection, nice graphical reporting. Free licensing available for Educational or OSS use. 
Similar to CPD 
Commercial 
  Simian  - fast, works with Java, C#, C, CPP, COBOL, JSP, HTMLSimscan  - free for open source projects 
High level reporting 
  XRadar  - Agregates data from a lot of code quality tool to generate
a full quality dashboard.Sonar  - Pretty much like XRadar, but younger project, fully integrated
to maven 2 (but requires a database)Maven Dashboard  - Same kind of agregator but
only for maven project.QALab  - Yet another maven plugin…