Super troopers
Sergio Leone's Once Upon A Time In The West has an amazing opening scene.
"As far back as I can remember,I always wanted to be a gangster....."
I also think 2001: A Space Odyssey has a great opening, even if it is just men in monkey suits
Top Gun
The Dark Knight bank scene. Was classic and perfectly setup.
Saving Private Ryan, it's the best scene I have ever seen on film.
Star Wars
When that Star Destroyer came into view you knew right then you were going to see something unlike anything you'd ever seen before.