Continuity mistake: When Bella is in the parking lot at school in the beginning, Edward walks toward her. Bella's hair is neatly pulled off to the side. When he leans in for the kiss it is suddenly stuck to her forehead, and when Edward tells her Jacob wants her, it's suddenly back to normal.
Continuity mistake: When Bella goes to the Cullens' house for her birthday party, Alice takes the new camera that Charlie got Bella and takes a picture of Bella and Edward. But when Bella prints out the picture and puts it in her scrapbook, it looks nothing like the picture Alice took. Given we see the entirety of her visit from start to finish, there was no other opportunity for a different photo to be taken.
Continuity mistake: In the scene where Carlisle is treating Bella's wound there is a shot of the bowl where he is putting the glass from the wound. You see that there is one piece of gauze. He then starts stitching up the wound and when he lights the contents of the bowl, you see lots more gauze that he hasn't used in there.
Deliberate mistake: In the scene where we see Bella in her room looking out the window, the months are passing, but she is always wearing the same clothes.
Visible crew/equipment: In the scene where Bella walks toward the strangers on motorcycles, her mic wire is visible through her jeans.
Continuity mistake: After the scene where Jacob rescues Bella from the ocean, when they're driving home it's not dark outside as they're pulling up into Charlie's driveway. But once Jacob starts talking about Sam and Emily, it's darker outside. Even after they get to the door.
Revealing mistake: When Edward takes his shirt off on the steps in Voltaire, his nipples are different colors and sizes. The closer one is grey while the far is more pink as though the makeup had rubbed off.
Revealing mistake: In the scene of the fight in the chamber of the Volturi when Demitri throws Edward on the stairs you can easily see the body of Pattinson's stunt double, there's a clear six pack, a tanned body and no body hair.
Visible crew/equipment: In the very last scene, right before the ultimatum, if you look into the tail lights on Edward's car you can see various members of the crew reflected.
Visible crew/equipment: In the scene when Edward left Bella, when Bella is running after Edward, you can see the shadow of a crew member briefly on the tree.
Other mistake: In Volterra when Edward has his shirt off, his face and neck are a different color than the rest of his skin.
Continuity mistake: Bella just went back to the meadow and is talking to Laurent. Throughout the whole scene in the meadow, her hair changes on her right ear. It goes from behind the ear, to fully covering the ear, to half covering the ear, and back and forth between those. And in the beginning, her hair is near perfect, but by the end, her hair is more wispy and not-so-matted to her head.
Continuity mistake: Right before Jacob comes through Bella's window, it shows her sleeping and "dreaming" of Victoria coming to get her. If you look, the camera really focuses on the dreamcatcher and how it's hanging above her on the bedpost. It is hanging off to the side of the middle hump. Immediately, Jacob comes through her window and focuses in on the dreamcatcher hanging on the bedpost which is now neatly hanging in a completely different way, perfectly laid over the center of the bedpost.