I know this isn’t really what you were asking, but I tend to prefer sex scenes that actually manage to advance the plot in a significant way. I can think of a few excellent examples:

Don't Look Now (1973) - A stunningly tender, passionate, frank, beautiful scene that (for once) unambiguously celebrates the love of a married couple (Julie Christie and Donald Sutherland), though obviously in the aftermath of profound grief and loss. One of my favourite films of all time, by the way.

The American (2010) - Critics didn't like this slow, meditative film, but I loved it. There's a protracted sex scene between two characters which begins as simply a man who has hired a prostitute, but throughout the (very explicit) scene, they wordlessly fall in love. It is brilliantly acted (by George Clooney and the gorgeous Violante Placido).

The Terminator (1984) - This sex scene is obviously vital to the plot for reasons I won't spoil for the 1.5 people reading this who haven't seen the film, but I also love this scene because it is the culmination of Michael Biehn and Linda Hamilton's love story in fast-forward (as is appropriate, given the action-oriented nature of the film). It tugs heartstrings appropriately (at least mine - I'm a big softie).

Angel Heart (1987) - This deliriously overripe Faustian noir-horror oozes with atmosphere, not least in the eye-widening sex scene between Lisa Bonet and Mickey Rourke. It goes from sweaty and passionate to sweaty and bloody, and then just bloody terrifying - again for reasons I won't spoil.