When Will stops his stolen taxi and gets out as the parade is blocking away, there is a cab with the 5K20 tag sitting in the line about three cars back and one row to the right from him. In the next shot, he turns around to see the cab pulling around the corner.
When Will meets Riley in the bar, during the talk with the horny police officer, there is 0.00 on the cash register. After he leaves the chair and scene continues, there is already 6.00 on the register, but nobody touched it nor a register sound was present.
As Vincent is about to put Alison back into the trunk from her escape he is holding her hand talking about fingerprints and the FBI; as he does so the position of the syringe in his hand changes position with the different camera angles front up to down and then back to up.
When Will is first talking with Vincent on the cellphone on Bourbon street there is a blonde female drinking from a 'go-cup' standing directly in front of him in the close-up shot. There is a distance shot a few seconds later and she is no longer there. But a few seconds later we are shown the close-up shot again and she is still where she was the first time.
Early on in the film there is a shot of the King Louis cathedral, right before a cut scene to Cage being released from jail. The cathedral is in New Orleans while the jail is clearly marked as a Texas facility, not a Louisiana facility.
In the final scene, the characters describe a 10 pound lump of gold as being worth $300,000. If the gold is worth $30,000 per pound, the duffel bag containing $10 million in gold would have weighed almost 340 pounds, too heavy for the characters to lift and drag around. (At the actual Feb 2012 gold price, the bag would have weighed 400 pounds.)
(at around 1h 14 mins) When Will and Riley are in the sewer trying to flee, you can see Cage stop and wait for his cue, you can see a portion of his body behind the wall as Akerman turns the corner. He isn't moving and then all of a sudden starts to. Obviously he was waiting for his cue from the director, but wasn't totally out of the shot like he should have been.