The bestselling series will finally have its conclusion this July (21st specifically). While the series has its detractors, which are probably louder and more numerous only on account of its popularity, I think you must admit it has been a satisfying series. Rowling has done a great job evolving the story from something simplistic enough for a child to something tacking real serious issues like racism, bigotry, and the evolution from adolescent to adult without painting a rosy picture. Additionally, unlike some other fantasy authors, she had a plan and she stuck to it. You can tell as you read and the plot is revealed that she had planned out all seven books even before beginning the first. Each revelation is deliberate and each nuance potentially important in a future work. I will be sad to see it end -- she created an elaborate world where many narratives could dwell. However, I'm glad she always had a final resolution, and I appreciate that.
If you haven't caught up, stop here as spoilers do follow...
Here are some of my theories as to what lies ahead in DH --
RAB is not Regulus Black
I just believe it to be too obvious, however I can't come up with a better answer. There is a chance she might be referencing someone she has not introduced yet, but it wouldn't be like her. More likely she's referring to someone we already know, possibly by a different name.
Snape and Dumbledore planned his death together
Dumbledore was not afraid of death -- Rowling did a great job of conveying that point throughout the series. Therefore, Dumbledore could not have been pleading for his life on the ramparts. My guess is that he was pleading for Snape to follow through with the plan they had hashed out together before hand. Snape's fury is that he must play the scape goat and be hated by everyone. It will be interesting how this is revealed to Harry -- Pensive or veritas serum?
I believe Dumbledore was already dying -- When he destroyed the horcrux ring, Dumbledore says he was saved by Snape. The solution was probably only temporary one and Dumbledore knew his death was imminent and wanted to be sure it was used to the fullest advantage.
Snape was secretly in love with Lilly Evans which was his repentance
This will probably be revealed in more detail in a Snape v. Harry confrontation.
Harry will end up sacrificing himself to vanquish Lord Voldemort
Again, another popular conclusion, but I think it makes sense. This has bitter-sweet ending written all over it.