When Buffy walks away after defeating the Ubervamp, she's got on different boots than she had on during the fight.
When Buffy and Xander leave to locate the new potential in town, Dawn's hair is straight. When Dawn is talking to Andrew, her hair is curled. When Dawn is watching the final fight, her hair is straight again.
In the scene following the opening credits, Willow's hair on her pillow keeps changing between shots.
A cable can been seen extending from the door, pulling it back, before the Ubervamp breaks it down.
When Anya and Giles speak with Beljoxa's Eye, Anya's mouth continues moving when she isn't talking and her words don't match her mouth movements.
When the Potentials are all arguing in unison at the dining room table, Molly's voice can be heard but her mouth isn't moving.