I'd have to say that Pirates of the Carribean 2: Dead Man's Chest has had the best trailer I've seen in a while. I was satisfied enough after the trailer that I could have left the theater without watching the movie I came to see (X-Men 3).
Sorry ya'll, this trophy goes to Spiderman 2 as the best trailer of the last five years, followed in a distant second is Revenge of the Sith and in third place is Spiderman 3. I'll give Ghost Rider and Return of the King and Batman Begins as nominal attempts at being the greatest, but this is simply no contest.