The night of freaks...
First, I have no idea about the horcruxes. Nor do I know who dies. Mostly, I want to know if Snape is good. We can blame it on my irrational obsession with Alan Rickman (*swoon*), or possibly on the fact that Snape has been so intricately written that he truly could go either way. Regardless, I need to know. I promise, I will deface Rowling's Wiki entry if she doesn't tell us.
My theory: He's good. Dumbledore makes mistakes but trusting Harry with someone who could potentially be that bad is not his style. So, without further ado, Mir's Snape is Good theory:
Snape and Lily were in Potions together (we know this because Slytherin and Gryffindor are in the same classes). They are both talented in Potions, and Lily has a soft spot for Snape. Or, at least she pities him. I think Snape fell for Lily (duh), and in a desperate plea to gain her love, he used the love potion on her. The biggest supporting factor for this is that there are four major potions mentioned in book 6 - polyjuice, amortentia, Felix Felicis and veritaserum. We have seen, in great detail, three of the four. And we know Rowling likes to leave little clues.
I think Snape was caught by James and buddies drugging Lily with the love potion, and this is their motivation for "throwing him to the werewolves," so to speak. James and Sirius are cocky and egotistical, but something more than childhood spite must have occurred to have them risk Snape's life in such a horrific manner. In the end, James changes his mind, and spares Snape (much as Harry spared Wormtail).
So, Snape goes on to become a Death Eater, and James marries Lily. Everyone's fine until Snape hears part of the prophecy. He relays the information to Voldemort, and Voldemort decides the prophecy means Harry. My theory is when Snape discovers that he intends to kill James, Lily, and Harry, he asks Voldemort to spare Lily. Several things support this. First, Voldemort tries several times to spare Lily before killing her. We know from Cedric that he has no qualms about murdering, and doing so swiftly, so WHY spare Lily? We also know he "greatly rewards" those who are faithful. What if Snape's reward was supposed to be Lily?
Last part of the theory: Snape is remorseful, and when Harry pesters Dumbledore to tell him why he trusts Snape, for a split second, he considers it (Book 6). Then he decides not to. Dumbledore has his reasons, and obviously, he thinks Harry can't handle them. And Snape being in love with his mother is certainly something he can't tolerate. I also think Dumbledore assigned Snape to Potions as a reminder of his penance.
I don't doubt that Snape hates Harry. He hates him for what he is, for what he's done, and for where he comes from. However, he's bound to Dumbledore to protect Harry, and assist him in his final task. Even if that means killing Dumbledore. And even if he hates Dumbledore for resigning him to such tasks.
Other theories:
One of the twins dies. There's been a lot of foreshadowing - profitable shop owners disappearing, the twins' business ties to the Ministry, their blatant disregard for Voldemort.
The house elves are crucial to Harry's conquering Voldemort. They're the most powerful of the magical creatures, and Dobby has been instrumental in assisting him along the way.
In one of Rowlings interviews, she stated that Ginny was the most powerful witch, being the 7th child whose parents were both 7th siblings. I have a feeling her power will shine through in this last book, making her a worthy adversary.
And that's about it. I'm sure there are other small tidbits that help in strengthening my debate, but seeing as how we'll know the truth tomorrow, I figure this short essay should suffice.
Oh, and unlike the FREAKIEST nuts, I will not be getting my book at midnight. Mine will be delivered by Muggle mail some time this weekend. I still have to get through Book 6 once again. So please, PLEASE don't spoil it for me. Mmmkay?