I've been waiting for The Dark Knight with white-knuckled anticipation, and as part of the viral marketing that began as early as January, they've released a terrifying and awesome interactive feature: committing your friends to the mother of all fictional insane asylums, Arkham Asylum.
I like that this kind of online marketing is becoming de rigeur for films, like with The Wackness's graffiti contest.
This is pretty sophisticated; you upload a headshot of you or your friend, and then it's integrated into a video, which shows creepy real-looking footage of that person then become a raving loony, writhing in a straight jacket.
Except I made the poor decision to test it out with my picture (Alcatraz flashback!) Permanently scarred.