Hey, It's That Guy!: Michelle Monaghan has a blink-and-you'll miss it role as one of the demons. She's the one who says, "Holy water...?" before they're all killed by the fire sprinklers. Her role was intended to be larger, serving as Constantine's demon lover, but her part was cut from the final film.
A lot of fans of the film (and comic) consider the editing out of Constantine's half-demon sex partner Ellie, based on the succubus Ellie from Hellblazer and played by Michelle Monaghan, to be a loss for the film. The reason given was that it would be harder to believe that Constantine was a bitter loner if he was sleeping with a gorgeous woman, even if she was evil.
Also, the deletion of many scenes from the original script which dealt with Chas' character. Even if you aren't fond of Shia LaBeouf, the original script gave his character something to actually do, whereas in the final film he disappears for a good two-thirds during the middle, which begs the question why his character wasn't also cut.
For the TV series, Liv staying for the actual run instead of being replaced after the pilot.