Favorite trailer... has to be the Bayonetta TGS 2008 reveal. It's a bit gratuitous (which probably makes it NSFW? :P), and it's atleast 50/50 not-ingame footage... but it conveys exactly what the game is. The speed, the insanity, the humor, the music.
If you don't like this trailer, Bayonetta probably isn't interesting to you?
Really shows off the character, how she's fully in control at all times. Not so much a fan of the gratuitous parts, but I don't mind them that much.
Can't think of any other reveal trailer that has taken me from not knowinig what a game is to deciding I had to check it out as quickly. (though there are many good ones in this thread).