I've had a few, but two come to mind.
1) Shortly after I had purchased my DVD player and could finally experience Dolby Digital back in early 1998, I played Air Force One. The scene when the F-15s sweep around Air Force One and sound goes around the room brought a huge smile to my face...many, many times as I continued to replay it.
2) After I got my PC13-Ultra hooked up, and I watched Mr. and Mrs. Smith. I had never felt anything in the movie...until then. When Brad Pitt is driving the dune buggy, he jumps a hill and lands. I felt that with such impact that I couldn't believe how great it sounded and felt.