GCViewer

GCViewer is a free open source tool to visualize data produced by the Java VM options -verbose:gc and -Xloggc:. It also calculates garbage collection related performance metrics (throughput, accumulated pauses, longest pause, etc.). This can be very useful when tuning the garbage collection of a particular application by changing generation sizes or setting the initial heap size. See here for a useful summary of garbage collection related JVM parameters.

http://www.javaperformancetuning.com/tools/gcviewer/index.shtml