Some kind of leak detection and tools to identify more clearly their origin.
We currently have heap profiling tools which implicitly allow us to see between to snapshots what may have been created but not released. A more formal tool which allows us to see specifically which developer-created objects have been retained, perhaps as an additional view to the heap profiler, would be ideal. That way a developer can do some actions and easily see where they may have leaks.
*** This bug has been marked as a duplicate of bug 17241 ***