The protagonist in this movie carries a Heckler&Koch MP5. In at least two scenes (after approximately 52 minutes) the director inserted random close-ups of a AR15-type weapon being shot. Not only do these two rifles look nothing alike, even the backdrop is radically different (the actual scene is set in a back alley, the close-up footage in a forest).
When Dacascos parks his car right outside the dead-guy's grocery store, the car faces towards the entrance door. When he leaves the store and gets in the car, the car now faces the direction where he wants to go.
Throughout the course of the film, the bombs set around the city count down from 48 hours until the city is destroyed, but during the last 10 or so minutes of the film, one shot of the bomb timer shows 40 seconds and clearly counts up to 43 seconds before cutting away. The timer then continues counting down.
Renchard is reading a book and his eyes start closing because he is sleepy. We can see at the left page an image of the statue of Hercules. When he wakes up you can still see the image, but when he puts the book down the image is not there and now on the left page there are letters.
There is a scene where Renchard is running out of an old garage that he's been in before after being spooked. As he leaves, he hits one of a set of double doors and it opens and closes behind him. Clearly the garage doors are both closed. He hops in his car and turns to face the door, gun ready in case anything comes out. Both doors are now as wide open as they can be and in fact are clearly propped open with sticks.
During the initial fight scene with the zombie/vampires, Renchard is about to set a creature on fire that's hanging upside down, there is a VERY noticeable shadow on the ground, like another creature is coming after him, but no one appears. It had to have been a crew member walking in front of the spotlight.
Vincent said they knew about Renchard rigging all the bombs to blow up the city and also about Renchard not wanting to rescue Brianna due to the risk of the city blowing up and killing them both. It then makes no sense for Vincent to create a mission to "save" Brianna, only to then kill her once they escaped. He could have just let her stay "un-rescued" and she would have died in the explosion anyway.