Carlisle Cullen is a memorable character too. As the head of the Cullen vampire family, he has a strong moral code which is unusual for a vampire. He tries to live a more 'human' life among his kind, and his guidance and wisdom play an important role in the family's dynamics and how they interact with the human world.
Edward Cullen is definitely one of the most memorable. His brooding and mysterious nature, combined with his vampire abilities, make him stand out. Bella Swan is also very memorable as she is the main character through whose eyes we experience the story. Her naivete and determination are notable traits.