Continuity mistake: In Olivander's shop, the packages Harry put down when entering the shop change position between shots. (00:24:30)
Revealing mistake: When Harry, Ron and Hermione are making their way back to the Gryffindor common room, Ron says 'She knows more about you than you do', to which Harry replies 'Who doesn't?' The "solid brick" staircase moves so that they have no place to go but the third floor forbidden corridor. If you pay attention to the staircase it can be seen that there is a good gap between the staircase and the one it connects to when it moves and that when Harry, Ron and Hermione run off the staircase to the corridor the staircase made of "solid stone" does an awful lot of shaking. (00:58:40)
Continuity mistake: When Harry Ron and Hermione first encounter Mrs Norris, she sits down. When they run off, she is stood up. Note her shadow. (00:59:20)
Other mistake: Percy Weasley is obviously talking to the Gryffindor first years when they first enter the Gryffindor common room, but there are too many first years. There are 5 boys and 5 girls in each dormitory, so 10 first years in each house, but in the shot there are obviously almost 20 students there, not including Percy. (00:47:30)
Suggested correction: While each room does only fit 5 students at a time, the movie did not state there is only one room for each gender per year. We don't see all of Gryffindor tower and have no way of knowing if there is only one room for first year boys/girls.
