i too like many people here believe that snape loved lily.the problem with this is that we have no proof.but on careful reading we get some hints which may point to snape loving lily.here are those hints:
'a girl was laughing as a scrawny boy tried to mount a bucking broomstick-
"ENOUGH"
chapter 26,seen and unforeseen,ootp.
this is the scene in which harry breaks into snape's memories.who is the girl playing with snape?lily?
coincidence or not harry repels snape when cho comes into his memories while snape repels harry when the girl comes.see how all it fits if we assume the girl to be lily.
lily and snape were childhood friends(neighbours?).snape who had a terrible childhood had a good time with lily.snape on one such occasion talks about his father and why he hopes to see his father in azkaban with dementors.petunia overhears this conversation.what i am saying is that snape is 'the awful boy'.the thought of using magic to send ones parents to jail must have frightened petunia and might be the reason for her appraoching dumbledore regarding dudley's magical powers(jo said that they exchanged letters)petunia makes an agreement with dumbledore that in return for her accepting harry,dumbledore must ensure that dudley doesn't perform magic(remember dumbledore in ootp says that he made an agreement with petunia).but since dumbledore is dead now dudley begins to exhibit magical tendencies.he may be the character who performs magic quite late in life as said by jk rowling.
These things may be off topic but i mentioned them to say that all things fit if we assume that snape loved lily.also many other things like why voldemort offered lily many chances to live and why dumbledore trusted snape so much can be explained if we assume this theory to be true.

I believe that Snape had feelings for Lily also. I am not sure what type of amorous feelings they are.

I think that Lily and Snape, being in many of the same classes and being of the same caliber would have been thrown together to help each other study. Lily was nice and as Lupin said, didn't look at what the person looked like but what they were (paraphrased and was that movie and book or just movie?). She wouldn't have judge Snape on his nose and hair (underwear maybe? ).

Snape appreciates those with talent and desire. He has said numerous times that he only wants to teach those who have talent. He is a gifted person and doesn't understand those who don't just 'get it' but have to think about it and study it. He would appreciate her talent.

Funny how he treats Hermione. She is the top of her class but knows it all through book learning and not natural talent as shown in potions class when Harry is following the Prince's directions and she freaks because it's not the way the book says...Does Hermione remind him of Lily and he treats her that way because he is reminded of Lily constantly?

There was probably an appreciation on Lily's side for Snape's abilities. Long nights in the library or other place of study - since they were in different houses, where?- telling eachother about family and experiences. She would have felt sorry for Snape's horrible background and might have felt a motherly sympathy. She might have even been able to appreciate him and possibly started liking him in other ways. I don't see a true, hard love yet.

They had spent time together and had been familiar. Snape was getting further in with the future DEs like Lucius. Lily didn't like this. A rift had started. When his worst memory happened things were a little strained between them. He was being humiliated in front of a large group of students and then she stepped in. This was far worse. He had already caught grief about haning around with her from his DE buddies. Now she was sticking up for him. He was so angry he used the Sectumsempra on James. She knew that things would end very badly and she performed the voiceless Levicorpus that he had tought her. He knew she had used his own jinx on him and it made him very mad. Snape reacted to the situation in his worst memory the way his parents taught him. He retaliated in the worst possible way. To hurt the one who was closest. He said what he said and that was the end of them.

That is my intuition about what happened between them. You are right that there is little in canon that comes out and says they were involved. There are enough hints to suggest it, just like Hermione and Ron.

Now in response to some of the previous posts:


Snape knows that Harry has some of LVs powers but he doesn’t know how much. Perhaps he thought better to safeguard himself.

Taking the memories out in front of Harry is one of two things. Either JKR needed to show us and almost all the books are - oh shoot, can’t think of the literary term – with Harry in them, from his point of view, third person, except Spinner’s End and the very beginning of PS/SS. So it had to be done in front of Harry...

The other is that Snape was taunting Harry. He wanted Harry to see these things to see how ‘evil’ his heroes were. Snape knows Harry and Harry’s quest for knowledge etc. He has to know that Harry will be drawn to those thoughts.

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Remus told Harry – and I’m sorry, I don’t remember if it was book, movie or both – that Lily didn’t like the fact that James cursed people, just because he could. She wouldn’t date him until he stopped, or she thought he had stopped. She must have made her feelings known when she saw him doing it. His favorite victim was Snape so she probably had commented on more than one occasion in regards to Snape. Thus the “I wont bother in future” line.

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Sirren mentioned, was it here or on the regular boards? That Snape had a bad reaction when he saw Harry's parents in Harry's mind. Snape did not think that Harry would remember them and was very shaken/shoked to see Lily. He was white and angry...Why else would he have had a reaction like that? Seeing Lily shook him to the core.

The simple fact that Snape never mentions Lily tells me, too, that he feels very strongly for her. He can't bear to let that out. He does not use it against Harry. He acts as if she never existed. She either hurt him gravely or he feels such remorse for causing her death that he cannot bring himself to even think of her. When she is thrust in front of him he loses control.

Reading between the lines is just as important as reading the lines. You get much more out of the book.

Cris

One thing that makes me ponder the possibility of Snape loving Lily is Harry's eye. Harry looks like his father except for his eyes. Snape hated James, so he hates Harry, but there are moments that Snape tried his best to save Harry. It's possible that Snape does know Lily from the childhood. It's possible that the horrible boy Petunia said is actually Snape, because James should be easily called "your father" in the conversation with Harry. I don't see Petunia has any bad feeling about James, thus she doesn't mind to look at Harry. It's possible that Snape does all for the Order because of his love to Lily. However, nothing is written clearly.
The strongest indication is definitely the Pensieve, as some posters already wrote. Why would Snape want to remove his memory before teaching Harry occlumency? What did he prevent Harry to see? It could be about his double agent status with Voldemort. However, Harry already knew Snape works for Dumbledore and that Snape was a Death-Eater. Nothing to hide here.
Also the snipet Harry saw in Book 5 is about Snape's childhood. It was related to James and Lily and Hogwarts. If it's about James' bad acts, why would Snape then ask Harry to rewrite all mishaps that James made at Hogwarts? If it's not about James, then it must be about Lily. Therefore, lacking of other clear proof, the hint that Snape loving Lily must be from this part.

Those of us who have read book 7 in its entirety have an answer to this question. Reactions anyone????