You know, I might as well go on record somewhere... here is my prediction for "Deathly Hallows". Possible SPOILERS here, and there are definite spoilers for the previous books!!!
Snape is good. He loved Lily Evans, and the reason that memory of being taunted by James is painful is not because he was embarrassed by Potter, but because he burned a bridge with Lily, forever, by calling her mudblood in a fit of prideful rage. He removed this memory from his mind specifically to avoid Potter seeing it. When Snape told Voldemort about the prophecy, he had no knowledge that it would be about Lily's son. He was truely remorseful for his part in their deaths.
Because of Potter's connection to Voldemort, Dumbledore ordered him (as he had with Mrs. Figg) to make time Harry spent with him unpleasant. It's not because Snape actually hates Harry (although he draws on his anger with James Potter to make the act convincing), it's that he can't afford to let Harry (and by their connection, Voldemort) see his love for Lily Evans. That would be a giveaway that Snape is in fact working for the Order.
I think the biggest clue to all this being true was in Half-Blood Prince. All three kids have watched Snape write instructions and notes before, yet they did not recognize the writing in the Potions book Harry found; as well, the handwriting appears to be a girl's. I believe it's Lily Evans writing, because she and Snape were both excellent at potions, I believe they were friends and study-partners until that unfortunate moment when Snape doomed his relationship with Lily by calling her Mudblood.
I also cite Hagrid's mention of the argument between Snape and Dumbledore (pages 405-406 in the U.S. hardcover printing). Snape didn't want to do something; Dumbledore held him to his agreement. I think this is a seed of evidence that Snape was in fact following Dumbledore's orders to kill him.
Edit: I also cite that, even when running from Harry (who was trying his best to kill him), Snape did not allow another Death Eater to perform the Cruciatus Curse on Harry. He said that Harry was for Voldemort to kill, but I can't imagine Voldemort actually having a problem with finding out his Death Eaters got both Harry and Dumbledore in one night.
And further, there is a very long pattern in the Harry Potter series of believing the worst of Snape only to have him turn out to be working for Dumbledore. Dumbledore dismissed all talk of Snape betraying him for a reason. While he may believe the best of people to a fault, Dumbledore is very shrewd, and I can't imagine he was fooled by someone he knew was giving information to Snape. I think Dumbledore knew Snape loved Lily, and that's what makes him sure he isn't on Snape's side.
THERE! It's on record; we'll find out this coming weekend!