One of my favorite sex scenes of all time (besides my own) was between Marlon Brando and Anna Magnani in a very dark 1960 film called "The Fugitive Kind".
I really don't remember that much about the movie, but I remember the scene. Marlon Brando played a drifter who comes to work at a store owned by Magnani and her somewhat sadistic, invalid husband. Magnani clears out a storeroom and puts a bed in it, saying something to Brando like "You might as well sleep here since you don't have a place."
Brando walked up behind Magnani as she was showing him the storeroom. From behind, he pushed her into the wall with his body and then kissed her neck. They were both fully dressed at the time. I know I moaned out loud right in the movie theater.
This was a film adaptation of a Tennessee Williams play. Williams' stories are always set someplace in the hot and sweaty South. He really is not one of my favorite writers. But this scene made me feel something on an emotional level.
Over the years, I've seen a lot of very "raw" sex scenes in movies. Some have worked better than others, for example, "9 1/2 Weeks" and "The Postman Always Rings Twice" and "The Piano". But none of those films have one particular scene that ever actually become embedded in my mind like the scene with Brando and Magnani.
There was a rawness and an honesty to the scene which was done by two very skilled actors who both "brought it" that day for that scene.
Perky breasts and bottoms don't make a scene sexy. Neither do graphic scenes without any emotion. Now, I like porn for porn's sake just as well as the next girl, but it's not really sexy. It's athletic, (usually kind of funny too!), but it's not particularly sexy.
Many years ago, Alex and I saw an amazing Japanese film called "Realm of the Senses". The movie featured mainstream Japanese actors and was a love story between a prostitute and a man. What distinguished this film from any other I've ever seen was that perhaps a full three minutes of the film actually showed graphic sexual penetration.
It was probably the most honest portrayal of sex in a relationship I've even seen on film. I found it somewhat surprising, but not nearly as stimulating as the sex scene in "The Fugitive Kind". My imagination provides much hotter sex than graphic portrayals on screen.