Visible crew/equipment: When Robocop visits Cain's hideout and sends his car in as a decoy, after he returns to the car, watch the driving shot closely. A wire has magically strung itself across the entrance and attached itself to the back of the car - it wasn't visible from an earlier shot. As the car drives forward it stretches the horizontal wire, and just as a tiny amount of pressure is exerted, the car explodes. Yeah, it's technically a mistake, but I think it's more worth checking out just to see how those tricky effects are achieved.
Visible crew/equipment: When Cain and his gang are making their escape from the drug factory at the start, we can see a crew members hand very obviously poking out from behind the door frame, giving the actors their prompts when to go.
Visible crew/equipment: At the start of the film, RoboCop is in his police car, and it gets hit with a rocket and it flips over, and then slides to a stop. It is quite obvious that RoboCop is not in the front of the car, and that a silver plate has been placed in the driver's seat to make it look like he is.