Revealing mistake: In the last scene where Edward and Bella are sitting in the sunny field, Edward is not sparkling.
Continuity mistake: At various times during the movie Bella's hair is different (she is wearing a wig due to her hair being cut for her role in "The Runaways"). You can notice it from the high angle when she walks to her truck the first time she goes to see Jacob, then various times during the movie her hair seems to be darker sometimes and her hairline moves as well.
Revealing mistake: After killing Victoria, Edward rips off a piece of Bella's shirt to tie around her bleeding arm. If you look at where he rips her shirt, the seam is visible where the fabric has already been cut and loosely reattached; there is a long horizontal wrinkle where it doesn't hang right from the rest of the shirt.
Continuity mistake: In the scene at the mountain campsite the camera pans out and shows that Bella is wearing brown cargo pants. When zoomed in again, she is wearing dark blue skinny-jean like pants.
Continuity mistake: In the "Be honest with me" scene, when Edward is trying to explain to Bella why she should not become like him, he states, "You'll always be my Bella". He sets his left hand on the right side of her head - in the first shot his left thumb is on top of her hair, when it cuts to a shot over Edwards left shoulder looking toward Bella his thumb is beneath her hair; cut back to the first shot and the thumb is on top of her hair again.