I thought it would be interesting to track Darcy's changing feelings for Lizzy up to Chapter 18. :D

"She is tolerable; but not handsome enough to tempt me; and I am in no humour at present to give consequence to young ladies who are slighted by other men. (Chapter 3)

In Chapter 3 Darcy does a good job of insulting Lizzy personally because he feels above his company—he disparages her appearance and her consequence. The first is nearly an unaccountable utterance as it becomes clear in the text that Lizzy is indeed attractive and the second is based only on the fact she is sitting down instead of dancing. He shows not one ounce of concern for her feelings or dignity although she is at least owed the common forms of curtsey as a gentleman’s daughter. Darcy is completely unfair to Lizzy. In short he dislikes her because of her status and he was in no humor to do so.

Mr. Darcy had at first scarcely allowed her to be pretty; he had looked at her without admiration at the ball; and when they next met, he looked at her only to criticize. (Chapter 6)

After the assembly ball and before the party at Lucas Lodge in Chapter 6 it is likely that Lizzy and Darcy met fives times over the course of a fortnight. One morning at Netherfield which I take to be a morning visit and dined in company with him four times—Chapter 6, the description on how many times Jane has seen Bingley. According to Darcy’s thoughts in Chapter 6 at these times he only looked at Lizzy to criticize.

Elizabeth looked archly, and turned away. Her resistance had not injured her with the gentleman, and he was thinking of her with some complacency, when thus accosted by Miss Bingley -- (Chapter 6)

By the party at Lucas Lodge Darcy has discovered to his mortification that he was wrong about Lizzy’s appearance and wrong about her manners and decides he wants to know more of her and towards the end of the chapter feels rather complacent about her. I think he feels complacent about her opinion of him, that she must like him. I think he takes her arch look for flirting with him. He is interested in her but I do not see an indication that he has particular designs on her.

Mr. Darcy said very little, and Mr. Hurst nothing at all. The former was divided between admiration of the brilliancy which exercise had given to her complexion, and doubt as to the occasion's justifying her coming so far alone. (Chapter 7)

When Lizzy arrives at Netherfield Darcy can only admire her despite her disheveled appearance and doubts about the justification of her cross-country trek and this continues to the height of defending his admiration of her fine eyes to Miss Bingley in Chapter 8, they were brightened by the exercise.

Elizabeth, having rather expected to affront him, was amazed at his gallantry; but there was a mixture of sweetness and archness in her manner which made it difficult for her to affront anybody, and Darcy had never been so bewitched by any woman as he was by her. He really believed that, were it not for the inferiority of her connexions, he should be in some danger. (Chapter 10)

In Chapter 10 Darcy begins to feel a particular attraction to Lizzy above any other woman he has ever met. I think it is the narrator which labels Darcy’s attraction as “bewitched” but Darcy believes her connections will prevent a higher regard for Lizzy from forming. Darcy does not admit to himself that he is in any danger from Lizzy but I think the narrators description of bewitched suggests he has lost some control over his feelings for her.

Her sister made not the smallest objection, and the pianoforte was opened; and Darcy, after a few moments' recollection, was not sorry for it. He began to feel the danger of paying Elizabeth too much attention. (Chapter 11)

Lizzy and Darcy nearly come to name calling in Chapter 11 over the faults of their particular characters but this does nothing to detract from Lizzy’s appeal to Darcy. She challenges him where Caroline has let herself become a door mat in her sycophantic catering to him. I think all of Caroline’s efforts to gain Darcy’s attention during Lizzy’s Netherfield stay only increase his attraction to Lizzy.

To Mr. Darcy it was welcome intelligence: Elizabeth had been at Netherfield long enough. She attracted him more than he liked… (Chapter 12)

In Chapter 12 Darcy finally admits to himself that he is attracted to Lizzy more than he likes but feels nothing can come of it due to her connections. He has been worried that he was in danger of liking her too much and now that he admits this is the case he worries she must feel her power over him and may hope to increase it. I think this is a legitimate worry for if Lizzy did try to increase his felicity then surely Darcy, bewitched as he is, would not be able to resist but Lizzy does not know her power over him. Darcy’s worry is all hand-in-hand with his feeling of complacency about her from Chapter 6. Darcy tells himself that he must crush all of Lizzy’s hopes of influencing his felicity and to this end he scarcely speaks ten words to her for an entire day and even refuses to look at her when they are alone for thirty minutes. This not looking at her business seems to be necessary to Darcy’s ability to rein in his fancy. In Chapter 15 he still does not want to look at her and determines, “not to fix his eyes on Elizabeth” but she had no problem observing him and longing to know about the odd greeting between him and Wickham.

"I would by no means suspend any pleasure of yours," he coldly replied. She said no more, and they went down the other dance and parted in silence; on each side dissatisfied, though not to an equal degree, for in Darcy's breast there was a tolerable powerful feeling towards her, which soon procured her pardon, and directed all his anger against another. (Chapter 18)

Considering Darcy would not even look at Lizzy during their last two meetings is it a wonder he asked her to dance at the Netherfield ball? Darcy probably thinks he owes Bingley, his host, a duty to dance a little at the ball. I suppose he honored the Superior Sisters again and then Lizzy because I assume he still feels it would be a punishment to stand up with any other lady from the country and second I do not think he can help himself. Darcy parts with Lizzy after their dance aware that he has strong feelings for her despite the fact she brought up Wickham and questioned Darcy's behavior towards him.

That his two sisters and Mr. Darcy, however, should have such an opportunity of ridiculing her relations, was bad enough, and she could not determine whether the silent contempt of the gentleman, or the insolent smiles of the ladies, were more intolerable. (Chapter 18)