If Snape owed a debt to Harry, it was repayed in his first year when Quirrel tried to kill Harry during the quidditch match, and Snape said the counter-jynx...So you can strike Snape from you list of DE's with a debt to Harry
![:-)](./images/smilies/icon_smile.gif)
There is, on the other hand, still Peter.
In our experience with snape, it's more customary for him to GLOAT when he wins, when he accomplishes something, or hell, even when he makes fun of some one (usually harry) in a rather clever way. And there is no doubt at all the he is the HBP as he said he was, and that was the only way he would have even known the name to begin with. What I dont get is, WHY does Voldemort want to kill Harry for himself? is it not enough to just have the kid dead. Why not just say "Hey, if you see him, feel free to kill him.".
The thing that leaves absolutely no room in my mind for any trace of doubt about snape being a good guy, is his reaction when Harry called him a coward. The only way you could descibe Snape after the scene with Dumbledore is cowardly...unless he was acting on Dumbledore's orders, which is why he had the look of hatred and revulsion on his face before he did it. And which is why he was so angry at being called a coward.