You know what movies could use zombies? Any one of those cheesy "vampires vs werewolves" movies. Underworld? Could use zombies. Twilite? Could DEFINITELY use zombies. True Blood? Zombies (though the way the series is going they could introduce zombies without skipping a beat).
Saw Twilight Friday night. It already has a bunch of zombies in it. They're called "the cast" .