The Army Intelligence Meeting Scene
I don't know if it's just me, but I absolutely love that scene.
It's supposed to be just a transition scene between the action-packed opening and the rest of the film, but it's so brilliantly executed. We are introduced to the main plot of the film, the role the Nazis play in this, Indy's love interest (and his academic life)... and the way the Ark is introduced with that picture is so intriguing and engaging.
It's also the first time we hear that little orchestral piece by John Williams when Indy opens the book. Still one of my favourite music tracks in history of film.
As far as "exposure" scenes go, this is as good as you can get. Today's producers wouldn't allow scenes like these to make the final cut. "This is just a bunch of people talking, we need to make them fight against a... polar bear or something to keep the audience engaged".
Spielberg, Lucas and Kasdan did a brilliant writing job there.