When Rachel is being terrorized by the jocks, she looks outside the door. When you see her look out the door from behind, she has her arm on the inside of the door frame, but when the shot changes, her arm is at the front of the door frame.
When Monica sees Rachel at the the make-up store in the mall, she goes over to say hi to Mrs. Potter the cashier. As Mrs. Potter walks away and Monica starts talking to Rachel, from the back shot of Monica, we see that she is adjusting the glasses on her left ear. When the camera goes to the front shot of Monica real quickly, she isn't adjusting them anymore.
Jesse has a burn on his right arm and hand from the battle at the end of the movie. When he is sitting at his desk, the burn completely covers his right hand, when Rachel walks in, the burn stops at his wrist, and his hand is fine, but then when he wakes up, the burn on his hand is back.
The first time we see the tape of Rachel and Jesse having sex (during the party on the large TV screens), the shot is from the right side of the bed (the bed header is to the right). Later on, when we see the tape again (Rachel hears when Jesse say he loves her, playing the tape and rewinding it several times, increasing the zoom each time), the shot has moved to the opposite side of the bed (similar in location to where the camera is located right after that scene took place when we first see him tell her he loves her).
When Sue Snell is talking to Rachel in the ruins of the old school, she tells Rachel that her telekinesis is a recessive gene disorder, which was passed on from her father. However, since Rachel is a female she has 2 X chromosomes, therefore her mom would have had to be a carrier of that gene also for it to show up in Emily, or she would just be a carrier also and her telekinetic trait would not show up.
During the ending battle sequence, Rachel gets shot with a white phosphorus flare gun, and falls into the swimming pool. When she falls in, the flare is extinguished by the water, but white phosphorus flares will actually continue to burn under water.