Sometimes, movies are masterpieces, but their trailers just plain sucks. But it also happens that the trailers are watchable in itself. Here's some of my favorites:

1) KAMIKAZE GIRLS (2004)
The unlikely friendshop between two girls with opposite lifestyles: One is a biker, the other devoted to lolita fashion. I love this offbeat movie, and the trailer is a total sugar rush.
https://www.youtube.com/watch?v=cbFEPS8PPic

2) CUTIE HONEY (2004)
The movie catches the magic of the original anime series. Just stupid, innocent fun!
https://www.youtube.com/watch?v=WZBiiCFU0j4

3) HAUSU (1977)
This is the strangest slasher movie I know. It makes BLOODY PIT OF HORROR looks mainstream. After the manuscript was written, the movie was put on hold for 2 years as no director would touch it. The trailer gives a good idea of the nature of the movie:
https://www.youtube.com/watch?v=iZugt3fiBe0

4) LITTLE INFERNO
Grotesque and ear-catching teaser for LITTLE INFERNO, one of the best toy-burning simulator games. No seriously, it's a great game!
https://www.youtube.com/watch?v=BbVC1iUTFEM


Feel free to add your own favorites!