[On a formatting note: I've tried to both embed the trailers (where possible) and link to the trailers someplace where I know they won't be pulled. If there's no embed, blame YouTube. Just click the link on the movie's title and you'll get it.]
1. Sin City (2005)
I can't tell you how excited I was the first time I saw this trailer -- and for someone who had zero familiarity with the books, was only so-so on Robert Rodriguez, and thought the cast was an unwieldy mess, I was not a terribly easy get. The whole thing is executed perfectly, from setting the mood, to introducing the three main characters (Rourke, Willis, Owen), and by the time we get to that laundry list of a cast, I was in. The music was good enough to make me download that song by The Servant -- a mistake, but a fitting one since this trailer seemed to make everything look a bit better than it was.
Awesome trailer attributes: cool song/score
8. Watchmen (2009)
Naturally, it's the initial teaser trailer I'm ranking -- I've talked about it on the blog before, so I guess you could just read that, but to review: The blueprint for how to introduce an adaptation of a beloved known quantity to fans while giving newbies just a taste to get them curious. Many, many, many bonus points for use of the Smashing Pumpkins song (which was, to remind you, a rejiggered version of the song that appeared on the soundtrack to the geek-despised Batman and Robin), one of the ballsiest maneuvers in trailer-making I've seen.
Awesome trailer attributes: cool song/score; teaser; great tagline