Flaw Detector - In beta, does control/data flow analysis to detect NullPointerExceptions
JStyle - $995, nice folks, lots of metrics and rules
JTest - 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 checks
SolidSDD - 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, HTML