1. The search for the Lords' swords. The movie created a plot line where, in order to defeat the darkness, Caspian needed to collect the seven Lords' swords and place them around a magical table. I did feel this took away a bit the importance Caspian felt in finding the Lords. It was more about his father in the book than in the movie.
2. The appearance of the White Witch. In the movie, she tempt Edward, beckoning him to her. She's not around in the book.
3. Eustace's transformation into a dragon. In the movie, he's transformed and remains that way for the remainder of the movie until they reach Aslan's Country. They use this as his redemption moment. He fights against the darkness and becomes a valued hero. In the book, he's a dragon for one night and it's in this night that he becomes humble. In the book, there was no need for redemption.
4. Aslan's Country or The Very End of the World. In the book, Reepicheep travels to the end of the world to save the last three lords who are in an enchanted sleep. In the movie, Reepicheep decides his adventures are done. Aslan is there and offers anyone of them a chance to enter Aslan's Country with the notion that if they do so, they cannot ever return.