Back in 1996 there wasn't an Internet telling you 3 years in advance about new movies. The first whiff of ID4 anyone got was during the Super Bowl. I was a senior at A&M and I remember watching it at a friends' house and me and the other sci-fi nerds being like WHAT WAS THAT??? when the tease aired.
Went to see Space Jam and saw the Star Wars Special Edition trailer - I think this was also released in 1996. Granted they had 3 of the best movies of all-time to make a trailer from, but this might be the best thing I've ever seen. Seeing that X-Wing blaze through the screen and the purposeful leaving of Yoda for the very last shot is so awesome.
First Phantom Menace trailer. My dad, my brother and I went to see the Waterboy on a Tuesday night because they promised to show the TPM trailer before and after the movie. I watched this trailer so many times on a VHS tape of it airing on Entertainment Tonight I could write a scene by scene description in my head including Mary Hart's intro of "Here's your ticket for a ride back to the future with Star Wars Episode I The Phantom Menace!"
First teaser for LOTR. If you were any level of fan of those books going into the movies, the sequence of the Fellowship appearing one by one through that little mountain pass is like waking up on Christmas morning and finding the present you've been wanting your whole life is under the tree. Perfectly captured.
I don't remember what movie I saw this in front of, but you could hear a majority of the audience in tears after it aired. The very best of what we can be.