I have all four of the core rule books and I am considering supplements now.
What do you consider the most essential supplement for the nWoD lines?
Why do you consider it so?
How often have you used it and do you consider the price worth it?
I've looked over most of them and have yet to find anything that I absolutely had to have. My biggest objection is that about half the books, and curiously the ones that have been most highly recommended, are setting and scenario related. I honestly don't need any help in those areas. I've got bushels of story ideas and NPCs.
Sell me on what you think is best.