And here is what I think regarding Snape.
Dumbeldore knew he was going to die. Either by Snape's hand, or by Draco's. Here are my points.
1. Dumbledore trusts Snape. We have never seen Dumbledore's trust fail, we have seen him admit to making mistakes, but that was about telling Harry information at a young age.
2. Snape is spying for the Order. In the second chapter he tells Narcissa and Bellatrix that he knows the Dark Lord's plan (to have Draco kill Dumbledore). Thus, it seems obvious that he would have told Dumbledore.
3. Dumbledore believes that nearly everyone can repent, and turn to good, thus he wants to try and save Draco before he kills Dumbledore and thus "ripping his soul in two". That is why Snape takes the Unbreakable Oath with Narcissa, on Dumbledore's orders. Snape will thus be able to save Draco by doing the deed for him.
4. Dumbledore knows he will die, so he begins giving Harry the private lessons, fueling him with as much information as possible to prepare him for the thruth of the final showdown with the Dark Lord.
5. Hagrid overhears an argument between Dumbledore and Snape. Harry takes it as an argument over an investigation into the houses, but I believe it is an argument about Snape killing Dumbledore.
6. I believe, that although in OOTP we saw Snape call Lily a mudblood, he probably didn't really mean it, afterall, he himself is obviously not pureblood. I believe that he had feelings for Lily, another reason to hate James, but ALSO A REASON TO FEEL REMORSE ABOUT THIER DEATHS, deaths he inadvertedly caused by telling the Dark Lord the first half of the prophecy, as Dumbledore told Harry.
7. Dumbledore would have died whether Draco/Snape killed him because of the poison he drank. The stuff had to have been rather leathal. Thus his dying deed was to save Draco's soul, in asense, by allowing Snape time to get to the roof and do the deed instead.
8. Dumbledore pleaded on the rooftop, but he did not technically plead for his life. He may have been pleading with Snape to do it, to save Draco, to save Harry, to maybe save the war, and to release him from the pain of the poison.
9. The look of hatred and disgust on Snapes face may have been for the following reasons:
a. I am completely wrong and he really is evil.
b. He hated and was disgusted at the deed before him.
c. He hated and disgusted himself for what he had to do.
10. During the chase afterwards, and the fight with Harry, Snape repeatedly told him to not call him a coward. I would have said the same (if I am right), because it would have taken the most courage in Snape to kill Dumbledore, one of the only men who ever showed him kindness, love, care, compassion, and TRUST. To kill a man who is technically sacrificing himself to save one his students, and even a student who never particularly liked him, but in the end did show signs that he did it only to save those he loves, Draco's mother andf Father.
Snape, if I am right, is not a coward, not in the slightest. He is one of the bravest characters in this series. I believe Snape will die in book 7, but not before all the truth is known. If I am right, Harry may learn not to hate Snape, at least not as much as he has throughout the series. He already has shown signs of being able to understand and pity Draco more, maybe, when it is all over, he will be able to do the same with Snape.
AHHH It was so good!
as their secret-keeper. I think the intelligence came from Snape. So it goes like this: he is in league with Voldemort, hears (part of) the prophesy, and reports it. Then he discovers Voldemort believes the prophesy refers to the Potters... and he tips Dumbledore off.
I don't think I can wait that long!
