Maybe "Space Seed: The Movie". Take the classic episode, a little retool, and you've got a movie. You could tell the basic story: Enterprise finds derelict ship, they revive Khan, Woos a female crewmember (Uhura?) he takes over the ship, and Kirk and Co. are forced to retake her before Khan uses the most powerful ship in the fleet (you know they'll go with that) to begin a mission of conquest. Maybe even toss Genesis and Carol Marcus into the mix as them working on a way to create a new Vulcan homeworld or something.