If you work with Core Data, you got to check out Core Data Editor. Remember Fred Brooks famous quote:
Show me your flowcharts and conceal your tables, and I shall continue to be mystified. Show me your tables, and I won’t usually need your flowcharts; they’ll be obvious.
It's true. I recently took over a project that uses Core Data and Core Data Editor lets me look at what are the types involved as well as data stored. It has a few handy features like letting you point to your simulator directory and
DerivedData directory so that it can automatically list your apps.
As of writing, there's a downloadable release on GitHub.