Mistakes are in no particular order. They are from:
1: When Hermione, Ron, and Harry return from their "date" with Fluffy for the first time, they pass through the painting. Harry looks back to check, and apparently, you can see a crew man's foot as a person is closing the door.
2: After final exams, we see that Hermione is wearing her grey school knee socks, but when the three of them run to Hagrid's house, we can see that Hermione is wearing white pantyhose.
3: At the start of term feast, after Harry is sorted into Gryffindor, he sits down on the right side of the table next to Ron. When the feast appears, Harry is on the other side of the table, next to Hermione.
4: When the three children get past Fluffy because the harp is playing, as Fluffy wakes he dribbles on Ron's shoulder. However, when they fall down into the Devil's Snare, his shirt is completely dry.
5:At the end of the movie Hagrid gives Harry the photo album. After Harry looks at it and tells Hagrid goodbye, he walks back to the train with his hands at his side and there is no sign of the album in either hand.
6: In the scene when Harry is in the restricted section of the library he walks in in the dark with only a lantern. He puts the lantern down in front of himself and begins to read. If you look at the bookshelf, his shadow is cast on the other side of the lantern as though the light is behind him.
7:When Professor McGonagall turns from a cat back into a human she isn't wearing her glasses, but in the next shot she is wearing them!
8: When Harry, Ron, and Hermoine get off the stairs (which have just moved) onto the third floor, the stairs bounce, clearly illustrating that they are not made of the hard stone they appear to be.
9: When Harry is looking at the snake in the zoo, it winks at him. This could not have happened since snakes do not have eyelids.
10: During the flying lesson when Neville's broom goes out of control, Ron covers his face with his hand. In the next shot, from above, both of Ron's hands are down at his sides.
11:When Harry, Ron and Hermione rush to Hagrid after end-of-the-year exams, and Harry is saying something that ends with "why didn't I see it before", Hermione is mouthing his lines.
12:In the Quidditch scene, Hermione's hair is crimped. Later, when you see the class looking at Neville after his fall, you see that her hair is striaght. The very next shot she's in, her hair's crimped again.
13:When everyone is outside for their flying lesson and Ron gets hit with his broom, he tells Harry to shut up. But if you watch Ron when he says it, you can see him smile and about to burst out laughing. It's not really a mistake, but it's pretty funny to notice!
14:In the scene when the kids first come in the great hall, on the table to right of the camera, you can see Oliver Wood. Next to him, there are some kids, but in the next shot, the kids are gone and Wood is on the corner of the table!
15.When Harry recieves his letter from Hogwarts, he opens it and it looks like one letter standard size. When the shot changes, it looks like a card (but we clearly saw Harry unfold it). And when they are in London, right before they enter The Leaky Cauldron, Standard size again but now there are more then one letter. Notice the folded left hand corner.
MORE SOON TO COME.