Thanks to Sarah for collecting these from Lostpedia.
Ben blows his match twice. The first time, the camera is positioned behind the candles, as Ms. Hawking enters the church. Then there is another shot from the other side of the room, where we see Ben performing this same movement.
The same photo (of two men at a slaughterhouse) is used both behind the counter and next to the door at Jill's butcher shop.
The oxygen tank that Jack uses to revive Sayid in the hospital is empty, with its indicator well into the red "refill" zone.
Sayid's hair changes from straight to curly.
The SUV's emblem is first taped over with black tape when Hurley gets pulled over, then is silvered over when they leave the gas station.
Source: Lostpedia