The profiler should be able to show retained size by class. Other heap analyzers can do this, and it really can show memory leaks that just the top 10 or 20 objects by retained size can't.
Initial version done in profiler-main
user: Tomas Hurka <firstname.lastname@example.org>
date: Mon Jun 25 14:05:53 2012 +0200
summary: issue #212357, initial version of Show retained size by classes
Integrated into 'main-golden', will be available in build *201206260002* on http://bits.netbeans.org/dev/nightly/ (upload may still be in progress)
User: Tomas Hurka <email@example.com>
Log: issue #212357, initial version of Show retained size by classes