Snape: Evil or good....or both

 Warning: Do not read if you have not finished the books because this gives away information.

In my personal opinion, I believe that Snape is a little bit of both. He may be malicious and hateful towards Harry, but that was because Snape was bullied by James Potter and James took Lily from him. Snape was also constantly protecting Harry every year, and Dumbledore had no doubt in his mind that Snape was loyal to him. Snape showed the utmost bravery in the Half Blood Prince when he killed Dumbledore because as you know, if you have read all the books, Dumbledore had to convince Snape to kill him. When it came for the time for Snape to actually kill Dumbledore, Snape almost couldn't go through with it, and Dumbledore had to beg for Snape to do it (though at the time it seemed Dumbledore was begging for his life). There is the fact that Snape was a Death Eater. Snape was sent to Hogwarts by Voldemort to be a sort of double agent, and once Snape was at Hogwarts he became a double agent for Dumbledore. You didn't really know for sure whether or not Snape was good until the last book when Snape gave Harry his memories. Then, it was shown that although Snape may have both good and evil, his love for Lily was the most important thing. Dumbledore always said the most important thing was love.

“But this is touching, Severus,” said Dumbledore seriously. “Have you grown to care for the boy, after all?”
“For him?” shouted Snape. “Expecto Patronum!”
From the tip of his wand burst the silver doe. She landed on the office floor, bounded once across the office, and soared out of the window. Dumbledore watched her fly away, and as her silvery glow faded he turned back to Snape, and his eyes were full of tears.
“After all this time?”
“Always,” said Snape.