3. The Dark Knight - "I Believe In Harvey Dent"
Viral marketing is the norm with movies nowadays, but few movies took it to such an absurdly complex and detailed level as The Dark Knight, a campaign that was both incredibly authentic-feeling and also a blast to sift through. The most prominent aspect was the use of countless websites, the most notable of which was the campaign site for Harvey Dent, which helped to popularise the phrase "I believe in Harvey Dent" before the film's first trailer was even released. To make things a little more interesting, these sites then began to be defaced by The Joker, helping to cement the conflict of the film in a more imaginative fashion than simply cutting and releasing a trailer. It gives these characters plenty of presence in our consciousness well ahead of release, which can never be a bad thing, and given that Batman himself is already well-established, he's allowed to take the back-seat to these two superb characters.