Continuity mistake: When Pinkman and White are having breakfast in the diner, the items on the table keep changing in each shot. Specifically, the jelly, the milk, the cup with the cream and, most noticeably, the rolled napkin with the cutlery inside: Sometimes folded, others opened.
Continuity mistake: Skyler makes Walt return the Challenger to the car dealership, but Walt decides to take it to a parking lot and spin donuts with it. Just before he crashes, he's spinning clockwise, starts to lose control, and tries to correct it by turning the steering wheel sharply to the left. However, from the overhead shot, the marks on the pavement indicate he was spinning counter-clockwise and tried to correct by turning right. (00:05:50)
Continuity mistake: When Walt is practicing his pistol draw in his apartment, he drags over a chair in which to sit during his practice. When he is dragging it, he aligns it directly against the carpet. However, a few seconds later, another shot shows that the chair is now inches away from the carpet, despite him never adjusting the chair.
Continuity mistake: When Gus starts to walk away from where he killed Victor, he drops the Box Cutter, and we see it landing. However, after a cut to the next shot, its position has changed. It is no longer sitting on the line in the floor, and it is pointing 180° in the other direction. We can also see from Walt's shadow that the Box Cutter has moved quite a bit further away from Walt. (00:35:05)