Firs things first... THIS trailer beats every other trailer ever. A horror movie trailer that doesn't tell you a f*cking thing. It just creeps you out and makes you wonder "wow, what the hell is that? I gotta see it!"
http://www.youtube.com/watch?v=ZFxgr8NTD20
I'm also fond of these:
The Videodrome trailer might be the only thing weirder than Videodrome:
http://www.youtube.com/watch?v=Fh5U2RW58p4
I love the old Hitchcock trailers:
http://www.youtube.com/watch?v=Ps8H3rg5GfM
I especially love the trailer for the Birds, which consists of Hitch talking about Birds, then out of nowhere, you see stuff from the movie and you just go "WTF"
http://www.youtube.com/watch?v=MZjaVdJt59U
I love 70s horror trailers.
http://www.youtube.com/watch?v=08U_JOv-6_Y
http://www.youtube.com/watch?v=zak1AUiOvLo
http://www.youtube.com/watch?v=k2DWutxndgk
As you can see, I like mostly old trailers. Back then making trailers was an art that was done very carefully. Now studios just hire outside companies to assemble them and make sure they hit all the same notes that make everything look just generic enough to make people interested and unoffended. Horror and sci-fi trailers make sure to show you everything... you see the monster in the trailer, its no longer just seen in glimpses (if at all). You see all the big action scenes, etc. There is no thought put into it anymore.
Also for you trailer fanatics, I can't recommend Joe Dante's
www.trailersfromhell.com enough. Its like a mini film school taught by all your favorite directors (there's a thread for the site here:
http://www.clubtokyo.org/discuss/viewtopic.php?t=16313).