F for Fake trailer (slightly NSFW - contains some nudity) At almost nine minutes long, this is actually more mini-movie than trailer. It was directed and edited by Orson Welles himself, largely from footage that never made it into the actual film.
→[More:]The result is an amusing short film that indicates and plays around with the themes of the movie.
Bonus trailer:
Citizen Kane -- another unique take on the typical movie house preview, this one also directed by Orson.