Just before James's SUV blows up you'll notice the wheels are different from when you first saw them.
When Reese is running up the spiral staircase following Wax, bodies are falling down the stairwell. When the 4th body falls down it makes Reese jump and some of the powder pops out of the vase he is carrying in his left arm onto his shoulder, in the next shot there is no powder on the shoulder.
When Wax and Reese are in the SUV following the waiter from the Chinese restaurant, the vehicle is wet, but in close-up shots of them inside the SUV, the windows are dry.
After shooting the terrorist, the blood splash patterns on Reese's face change between shots.
When Reese is at the sink to wash the blood off of his face after destroying the pushers' lair, he raises up and looks in the mirror after his first rinse off. There is still a large patch of blood on his left-top forehead. When it cuts to his CU, the blood isn't there and he hasn't washed it off.
Reece says he has a 9mm at the back of his car, however the pistol in his car is actually a Beretta Px4 and the model in the movie is chambered in .45 ACP.
In the final scene where Rush and Wax lay their pistols on the table, Rush's Desert Eagle has the legend "Made in Japan". All Desert Eagles are made in the USA, and this one is an imported Airsoft BB replica.
When Reese is watching for drug dealers through binoculars while Wax is in the other room with a hooker, you see Reese looking through the binoculars correctly. Shortly after, Wax takes over while Reese answers the door. Wax can be seen holding the binoculars back-to-front (inverted).
John Travolta was holding the binoculars backwards when He was watching thru the window.
When the SUV pulls up to the Chinese restaurant, you can see the police lights at the filming traffic barricade when the camera pans to the right.
When Charlie uses his watch to send coordinates to the satellite, the satellite zooms in on a location northwest of Paris. The coordinates Charlie sends (48.79, 2.337) are actually south of the city, near Orly Airport.
During the car chase Wax leans out of the passenger side window of the Audi, aiming his rocket launcher across the roof towards the terrorist's car, which travels on the driver's side.
In several shots it is clearly visible, that the Audi has a glass sun roof. This type of roof can always be opened with Audi. So rather than leaning at high personal risk out of the passenger's side window, it would have been the logical thing to do for Wax to open the sunroof which would have also provided a much better field of fire and be at the same time be far less risky.