When Cindy is going to enter the lighthouse, you can see that the wind has got some of her hair in front of her forehead. When inside the lighthouse, you can see when Cindy appears in the monitors that she has got her hair combed, and in a different style.
When George gets his head caught in the bus door, there is a bus stop sign between the mailbox and a tree right after. When Sayaman is pulling into Tom's Driveway right before they discuss the night of Annie's death, there is no bus stop sign between the mailbox and tree.
In the cellar scene, Cindy knocks over a jar of marbles and they all roll toward the center of the floor, along with some other items such as fruit. In the wide shot of the carpet, there are only marbles.
When the President drives up to Logan's farm, he runs over two aliens. He pulls two $10 bills out of his wallet to place on the body, but in the next shot when he places the bills on the alien, the bills have changed to $20 bills. In the following shot, the money is gone completely.
When Cindy starts hacking away at the floor when revealing the well, she makes the first hole in the center, but later on, we see her lifting up a large circular section of the floor, with no hole in the middle.
When Cody is coloring at his home a package of crayons is placed outside of black circle he drew earlier, and when it cuts to Cody and then back to place where the circle is visible, the package is right on top of the circle.
When Carson is dancing with the twins, you can see Britney Spears and Fred Durst dancing in the background. Carson is seen making out with a woman a few feet in front of Brit and Fred, but when the camera cuts to Cindy, she's looking towards Carson, and Britney and Fred are behind Cindy.
When Father Muldoon arrives to babysit Cody, the glass in the window is frosted and the visitor cannot be seen. When we next see the door as George arrives, he is quite clearly visible through the glass before the door is opened.
During Brenda's wake, at about 33:00, the grandmother (wearing a grey and black outfit) gets punched out by Mahalik and lands on the couch. During the rest of the scene, in the background, her position jumps from sitting to standing and back again. For example, when Brenda's underwear lands on her head, she is standing even though the previous cut showed her on the couch.
At the beginning of the flashback Father Muldoon is seen singing to the tune on the radio. In the next shot you can see the road behind him is clear. The following scene shows him exiting the car with two police cars clearly visible behind him.
Just after George leaves the classroom after picking up his niece, and the pens are thrown at the door, there is an arm throwing the pens and it is obviously not one of the kids, as just after that Brenda looks in the opposite direction (to the middle of the room) when she asks who threw them.
In one scene Becca rips of her shirt, showing her bra, and throws it towards the parrot. At the next scene she suddenly has all her clothes on. However at the start of that scene, as she comes up the stairs, she is seen buttoning a (presumably) new shirt
On their way into the rap battle, Cindy and Brenda walk through a metal detector. There is also an X-Ray machine to their right, apparently scanning for weapons. Despite this, every patron inside the club is carrying a pistol.
When Cindy drives away after the school scene when she forgets to put Cody into the car, the hybrid she is driving pulls away as normal down the road. But when she stops the car after driving for a minute, the car stops in the same place that it started. You can see this by the positions of the school bus and the same extras walking by the same spot once again.
The goof items below may give away important plot points.
When George gets his head caught in the bus door, the information on the mailbox says 4395 LOGAN. In a shot of the house right after Brenda's death and before George gets the phone call telling him that Brenda is dead, the mailbox reads 2191 LOGAN.
When George and Cindy are talking outside Brenda's parents' house at the funeral, and Cindy starts to cry, she hugs George. Her head is on his shoulder when the camera shows her face and George's side. When the shot changes, her head is under his chin. The next time the shot changes, her head is back on his shoulder. So basically, the placement of Cindy's head changes with each shot.
When the aliens are choking the humans, one of the guy says, "They must have some kind of weakness." He takes she shovel and knocks the alien's whole head off and he falls to the ground. In the next shot, you can still see a part of his head showing.
When the aliens are describing how they pee, and the shot cuts to the president, when his right hand is at his side, you can see the small black container in his hand which he squeezes on to pee out of a second later.