Can't find an intro clip for it, but Lesbian Vampire Hunters pretty much seals my vote with a hammer. Something something vampire lore, and wraps up with "And then he cut her fucking head off"
Dawn of the Dead (Snyder version). The opening through when the main character crashes their car was extremely intense and captured the end of the world catching people by surprise perfectly
The introduction to Up, which made the movie for most people. Pretty sure the entire theater was sobbing by the end of that sequence.
This one takes it for me. I remember seeing that in the theater in '99 and when the camera spins around Trinity, my jaw about hit the fucking floor. We take those shots for granted now because they were so overdone following that movie, but in '99? Holy fuckballs!
Of course everyone knows this film now, but when it came out, it was sooooo fun. Mike Myers is a comic genius, and this opening sequence always makes just feel good.