Deathly Hallows Epilogue (Spoilers, obviously)
I absolutely loved the 19 years later part, it was so emotive and felt like a really natural ending to the series. However, I have only one question that will be forever unanswered - What did Harry, Ron and Hermionie do for careers? I think it was a bit unfair of JK not to put this in, especially since she informed us that Neville became a Professor.