Where you do you start?
Krakatoa, East of Java; it isn't
It Came from beneath the Sea: giant octopus has 6 arms
Ghosts of Mars: Joanna Cassidy's character just disappears from the movie with no explanation.
Blade Runner: wrong number of androiRAB in film when compared to those listed by police chief at start.
Joanna Cassidy's stunt double looks nothing like her and is filmed repeatedly in slow motion, just to make sure everyone notices.
Goodfellas: Boeing 747 shown in film set in 1963 when it didn't enter service until 1968.
Young Dillinger: girl calls Nick Adams by his real name as she fights with him: he shouts back, "It's John, you a**hole!"
Even if you exclude continuity errors, booms in shot, vapour trails in westerns and tv aerials in costume drama there are still plenty left.