The answer above gives a good overview of round, flat, static, and dynamic characters in Pride and Prejudice. The main characters who are both rounded and dynamic (meaning that they change) are Elizabeth and Darcy. While Elizabeth is often associated with prejudice because she develops a dislike for Darcy after overhearing him say she is not good looking enough to tempt him to dance, she also exhibits pride in her angry refusal of his marriage offer. Darcy, often associated with pride because of his high social status and reserved personality, also shows prejudice against Elizabeth's family. Both characters need to grow in wisdom and humility before they can marry the other. Mr. Bennet, a flat character, is dynamic because he learns to be less cynical and disengaged about his daughters' upbringings after Lydia elopes. Kitty, the second-to-youngest sister, is a flat character who begins to become steadier and less giddy at the end of the novel under the guidance of her older sisters.
Charlotte, Elizabeth best friend, is a static but rounded character. She doesn't change in her outlook towards marriage—to her it is primarily a pragmatic partnership from start to finish, and as she tells Elizabeth, she doesn't look for romance. She marries the ridiculous Mr. Collins because he has income and status. While she doesn't change in her marriage outlook, she becomes more rounded as the novel progresses: we understand her more fully when Elizabeth goes to visit her after her marriage, and we learn to be more sympathetic towards her as we understand how thoughtfully she manages her life and household.
Mrs. Bennet is probably the novel's quintessential flat, static character. Her one thought, start to finish, is getting her daughters married and that goal, and her pride in achieving it, never wavers. Mr. Collins is another static character who remains a shallow sycophant from his first entrance in the novel to his last utterance.
Positive static characters include the Gardiners, the Bennet sisters' aunt and uncle, who act as stable parent substitutes, especially to Jane and Elizabeth, in contrast to the inadequate Mr. and Mrs. Bennet.
Pride and Prejudice has a large cast of characters, but the primary focus is on the growth in Darcy and Elizabeth, with most of the other characters less prone to change.