For me it’s the chariot race in Ben Hur. I don’t think I’ve even see the whole film but if it’s on I’ll always watch the race. It’s so freaking awesome - the constant rumble of hooves and wheels, the portrayal of the terrifying reality of Roman sport, the actual danger that the actors and horses were in when doing the filming, the decision to make a scene in a film so long, the horses, everything.
Another is when the Lancasters take off in Dambusters - not for jingoistic reasons (though they wouldn’t be totally unreasonable) but for the noise of the freaking engines, and the efforts in the face of adversity that were being made by people at that time.
A happier one is when Stewie Griffin dances with Gene Kelly.